Precept Is Latest Chapter In GM's Continuing Effort To Develop Advanced Technology Vehicles

January 11, 2000 - DETROIT -- General Motors today unveiled the Precept, a fully functional hybrid electric five-passenger family sedan designed to achieve 80 mpg. The Precept is the latest demonstration of GM's capability and commitment to developing vehicles that will ultimately take the automobile out of the environmental debate.

GM also revealed an advanced fuel cell system with chemical hydride storage packaged in a second GM Precept to take advantage of its extremely efficient architecture.

The Precept is an example of the type of ultra-high-efficiency architecture that GM is developing on its way toward putting millions of environmentally friendly vehicles on the road. But the story didn't begin with Precept; it began nearly ten years ago, with the commitment to build advanced technology vehicles and the introduction of the EV1, the world's first contemporary production electric car. The key to GM's advanced vehicles strategy is to create a number of more fuel-efficient transportation solutions and let the marketplace decide which options ultimately go to production.

"Three years ago, GM chairman John F. Smith Jr. spelled out our strategy of developing a portfolio of technology options for the future," said Robert C. Purcell, executive director of GM Advanced Technology Vehicles (ATV). "Some of those options were revealed at the 1998 North American International Auto Show when we presented an EV1 powered by advanced nickel metal hydride batteries, a parallel hybrid propulsion system and a fuel cell system supplied by a methanol reformer. Today, we are delivering the EV1 vehicles with nickel metal hybrid batteries. For tomorrow, GM is building upon the foundation of the EV1 experience, both in the lab and on the road with real customers, to create an even more efficient vehicle architecture, called the Precept.

The Precept evolved as a result of GM's involvement in the Partnership for a New Generation of Vehicles (PNGV), a joint effort between the US Government and the domestic auto industry that began in 1993. The specific aims of this Partnership are lower emissions and up to three times the fuel efficiency of conventional cars (i.e., up to 80 mpg) without compromising safety, performance, affordability, or utility. The timetable called for each partner's proof-of-technical-concept vehicle to be ready by 2000 followed by a production prototype in 2004. The Precept showcases the notable progress GM has already made toward the 80 mpg stretch target.

Whereas the PNGV parameters were the catalyst for Precept, the high-efficiency architecture and the propulsion system are a unique solution created by the General Motors innovation team. Moreover, the same technologies developed in the Precept program have been leveraged by other advanced vehicles at GM, including the flexible-architecture Triax unveiled at last fall's Tokyo Motor Show, and the high-efficiency, low-emissions G90 shown at Frankfurt last September. While these two vehicles may be mid-term solutions to the environmental issues facing the industry, the Precept hybrid and fuel cell versions are considered to be more long-term solutions. Nevertheless, in order to provide fuel efficiency and environmental benefits in the near-term, GM's objective is to transfer as many of the technologies as practical from all of these technology demonstration vehicles to GM's core portfolio of conventional vehicles.

Precept Feature Highlights: Technologies of the Future Today

Like a contemporary Chevrolet Impala, the Precept carries five passengers safely and comfortably. But it does so with nearly three times the fuel efficiency, a technological leap comparable to NASA's Apollo mission to the moon. In order to reap these remarkable gains, every major detail of the family sedan as we know it was scrutinized and optimized.

The dual-axle regenerative, parallel hybrid propulsion system features a 35kW three-phase electric motor driving the front wheels and a lean-burn compression-ignition, direct-injection (CIDI) heat engine driving the rear wheels along with a multi-purpose unit (MPU). Multiple energy-conversion devices are used for propulsion because that facilitates operating each in its zone of optimum efficiency. Sophisticated electronic controls interpret the driver's commands and manage every aspect of the propulsion system's operation.

The brain of the entire hybrid propulsion system is a power PC processor-based controller. This 32-bit, 266 MHz device conducts a two-way dialogue with the following equipment: accelerator pedal, brake pedal, PRND shifter, energy management system, electric traction system, multi-purpose unit, CIDI engine controller, transaxle controller, thermal system controller, and brake controller. As the driver's commands come in, efficiency and emissions optimization constraints are applied, and digitally coded commands go out. It makes snap decisions to optimize all operations, such as the highly intelligent heating and cooling system. Specifically, the system moves otherwise wasted thermal energy automatically to where it's needed -- it even anticipates when fog could form on the windshield and works to prevent it. Throughout the Precept, forty-seven distributed computer modules provide smart control to make this the world's most computerized vehicle.

A key component of the hybrid powertrain is a unique, high-efficiency, automatically shifted manual transaxle. To create the unit, located at the back of the vehicle, GM engineers began with a five-speed manual transaxle from an Opel Astra. By the time the design was finished, not much of the original gearbox was left. Fifth and reverse gears were eliminated (reverse operation is provided by the electric traction system in the front of the vehicle). Gear shifting via clutch was converted to an automatic, computer-controlled operation. As a result, the CIDI engine can be started in any gear, and skip shifting is also possible. In addition, the time required for a gear change, or to start the engine, is about 0.7 seconds. Most importantly, efficiency losses through this transaxle are substantially lower than what automatic or continuously variable transmission (CVT) alternatives would provide.

Another key benefit of the dual-axle, parallel-hybrid approach is that it offers maximum use of regenerative braking through all four wheels. When the driver lifts off the accelerator or taps the brake pedal, unwanted momentum is automatically converted to electrical energy and used to recharge the battery pack located under the front seat. That alone amounts to 13 mpg in combined city-highway driving, helping the Precept approach its target of 80 mpg. An ingenious multi-purpose unit handles regenerative braking through the rear wheels in addition to performing five other functions: it contributes 10kW of propulsion power when maximum acceleration is desired, it starts the rear-mounted engine, it powers the air-conditioning compressor when the engine is at rest, the engine can drive it as a generator to recharge the battery and it is used to synchronize the gears for clutchless shifting.

Two of the world's most advanced battery systems are being explored for use in the vehicle -- the world's first application of lithium polymer batteries for hybrid vehicle propulsion, and a new generation of advanced nickel metal hydride batteries designed explicitly for the high power encountered in a hybrid propulsion system.

The Architecture: Eye-Catching, Lightweight, and Ultra-Efficient

Aluminum is used extensively throughout the Precept's body and chassis components to reduce mass. Like the EV1, the Precept uses a light, stiff space-frame body structure constructed of aluminum stampings, extrusions and castings. Exterior panels are made of aluminum and composite materials. Bumper beams are fabricated with carbon fiber. The mass is 45 percent less than a comparable steel body design.

Since the weight carried by the front tires has been significantly reduced, no power steering assist is necessary. Computer-controlled air springs maintain a level ride height irrespective of passenger and cargo load changes. The springs' source of compressed air can be tapped to inflate the Michelin Proxima radial tires, which have a rolling resistance 10 percent less than the EV1's already low rolling resistance radials. The Precept's Hayes-Lemmerz wrought-aluminum road wheels each weigh only 3.8 kg, distinguishing them as the world's lightest 16-inch wheels.

The zero-drag friction brakes for the Precept weigh less than half as much as comparable hardware in today's Chevrolet Impala. An advanced brake-by-wire system uses a small electrically powered hydraulic pump located in close proximity to each brake caliper.

Maintaining a controlled ground clearance in conjunction with the use of a flat underbody, rear cooling air entries and exits, and other aerodynamic features -- along with extensive wind-tunnel tuning -- has resulted in the lowest drag coefficient ever recorded for a five-passenger, four-door family sedan (Cd = 0.163). So efficient is the Precept's shape that just the addition of conventional outside rear-view mirrors would increase drag by more than 17 percent. Consequently, the Precept employs two tiny cameras instead of outside rear-view mirrors which, when combined with a third rear-facing camera located inside the rear window, produce an integrated panoramic rear view on a reconfigurable LCD display easily viewed by the driver.

The Precept's interior is nearly as futuristic as its exterior and mechanicals. Advanced interior trim materials not only save additional weight, they also provide added convenience and an inviting appearance. An excellent example of this are the ultra-light front seats, which are 11 percent lighter than EV1's. The front seats consist of powder-coated steel and aluminum frames with a bare minimum of foam padding and trim materials for the bolsters. A mesh material serves as the center insert, for both the seat bottom and the seat back.

Instead of conventional padded carpeting, the Precept has a lower weight, resilient, rubber-textured floor covering. Overlay mats, removable for cleaning, are also rubber. Multiple storage areas eliminated the need for a glove box, which in turn allowed interior designers to lighten and simplify the instrument panel.

A Motorola-supplied Driver Control Center provides a unique driver-vehicle interface used to operate the car. To start and drive the car, no mechanical key is needed. Instead, the driver enters a five digit security code using the electronic key pad positioned below the display screen, hits the RUN button, and shifts the vehicle out of park and into forward or reverse gear using another set of push buttons.

A smart switch in the control panel operates like a mouse for the laptop computer docked at the top of the instrument panel. It is used to scroll through a menu displayed on the laptop screen. The screen is positioned far forward just under the windshield's base, so minimal refocusing is necessary when shifting between a view of the road and a check of the instruments. The screen display can be formatted as the driver pleases. Three distinct categories of information are presented: a view to the rear supplied by the three video cameras; vehicle operating data, such as speed and fuel remaining; and secondary entertainment and climate control system parameters.

In Conclusion: One More Step in the Process

The integration of revolutionary technologies into the Precept is just another step toward GM's ultimate goal of transferring advanced technology to its core product portfolio and ultimately removing the automobile from the environmental equation.

General Motors sees a definite business proposition in advanced technology vehicles. GM intends to lead the automotive industry into a more fuel-efficient and environmentally responsive age by building efficient and affordable vehicles that consumers will want to buy and want to drive.

GM has forged partnerships in both the automotive industry and the fuels industry that will speed development and help us reach our goals. Together with esteemed partners like Toyota, Isuzu, Suzuki, Exxon and BP Amoco, GM will lead today's automobile industry into tomorrow.