Cutaway view of
GM Precept hybrid-eletric concept
Designing a full-sized family sedan that achieves PNGV's goal of 80 mpg is a daunting engineering challenge, one which GM accomplished in the form of the landmark Precept hybrid-electric car.

Building The Precept

An Interview with Bill Shepard, Program Manager, GM Precept Concept Vehicle

By Bill Moore

07 June 2000 -- Developing the technology to build a full-sized passenger car that gets 80 miles per gallon (2.62 liters/100 km) doesn't come easy, but having built the EV1 battery electric car helped the folks at GM's Advanced Technology Vehicle (ATV) center in Troy, Michigan get a definite "leg up" on their Dearborn and Auburn Hills competitors, according to Bill Shepard, the program manager for the GM Precept.

The Precept is General Motor's response to Vice President Al Gore's 1993 challenge to develop a new type of passenger vehicle for the 21st Century, one that could deliver up to 100 mpg fuel efficiency and reduced emissions. Called the Partnership for a New Generation Vehicle (PNGV), the joint private industry, public agency partnership has led to the development of technologies that will eventually find their way into the cars and trucks of the new century.

ATV Enters The Fray

Bill Shepard told EVWorld.Com that it wasn't until 1996 that ATV got involved in the development of the Precept concept vehicle. Prior to that, he said a lot of groundwork had to be done to develop the necessary underlying technologies that would go into the Precept and its competitors, the Ford Prodigy and DaimlerChrysler ESX-series of hybrid-electric cars.

There was, "a lot of work with the government agencies lining up research and development that was needed at the various federal laboratories," Shepard stated. " There was a lot of component and system level development that took place early on that enabled us to have some features and some systems all geared toward generation of the highest fuel economy at our disposal when, the Big Three, sat down design these cars beginning about '96."

Taping Its EV1 Expertise

With the EV1 design and development program nearing completion in 1996, Shepard said GM "rounded up" many members of that team to begin work on designing the PNGV car that would eventually become known as the Precept.

"Fortunately, we had a cadre of people here that had just gone through that program that had many of the same priorities in terms of efficiency, trying to get the last mile out of every little bit of energy possible, which obviously was the same strategy that we needed to use in going into the PNGV program."

While the goal of the EV1 program was to wring out the maximum mileage out of a battery charge, the goal of the PNGV was to extract the maximum amount of energy from a given unit of fuel. What that fuel would be, wasn't yet known though all three carmakers would eventually settle on advanced diesel engines called CIDI (compression ignition, direct injection) because they offered a 15% improvement in efficiency over the best gasoline engines.

"We had some core expertise, as we call it, in electric drive and controls that we were able to immediately apply to the parallel hybrid task. We also selected an aluminum body structure strategy that also carried over from the EV1 and various elements of the efficient chassis design; going for lowest rolling resistance from the tires, for example."

From this point forward, GM's PNGV team proceeded "very deliberately," according to Shepard.



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