January 5, 2000
World premiere in Detroit
GM Precept: Concept Vehicle with Lowest Drag
Parallel hybrid drive – Advanced battery systems – Extensive use of aluminum
DETROIT - Opel's parent company General Motors will unveil the Precept, a fully functional hybrid electric vehicle with the lowest drag coefficient (Cd = 0.163) ever recorded for a five-passenger, four-door family sedan, at this year's Detroit Motor Show (January 15 – 23). The Precept is powered by an electric motor driving the front wheels and a turbo diesel engine with common-rail direct-injection driving the rear wheels. The parallel-hybrid propulsion system, managed by sophisticated electronic controls, helps the Precept approach its target fuel consumption of 80 miles per gallon (2.94 liters per 100 kilometers).
Two of the world's most advanced battery systems are being explored for use in the Precept - the world's first application of lithium polymer batteries for hybrid vehicle propulsion, and a new generation of compact nickel metal hydride batteries. Aluminum is used extensively throughout the vehicle's body and chassis to reduce mass.
The Precept is the latest demonstration of GM's capability and commitment to developing efficient and affordable environmentally compatible vehicles. It 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 US auto industry that began in 1993. The specific aims of this partnership are lower emissions and significantly improved fuel efficiency without compromising safety, performance, affordability, or utility.
Whereas the PNGV parameters were the catalyst for Precept, the high-efficiency architecture and the propulsion system are a unique solution created by GM. Moreover, the same technologies developed in the Precept program have been leveraged by other advanced vehicles at GM, including the high-efficiency, low-emissions Opel G90 shown at the Frankfurt Motor Show last September.
Precept Feature Highlights: Technologies of the Future Today
The dual-axle regenerative, parallel hybrid propulsion system of the Precept features a 35 kW three-phase electric motor driving the front wheels and a three-cylinder, 1.3-liter turbo diesel engine (40 kW/54 hp) with common-rail direct-injection driving the rear wheels. 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 PC processor-based controller. This 32-bit, 266 MHz device conducts a two-way dialogue with the following equipment: accelerator pedal, brake pedal, gear shifter, energy management system, electric traction system, multi-purpose unit, diesel engine controller, transaxle controller, thermal system controller, and brake controller. 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.
Key Component: Computer-Controlled Automatic Gear Shifting
A key component of the hybrid powertrain is a unique, high-efficiency, automatically shifted manual transaxle. 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 diesel 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 particularly low.
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 more than 0.5 l/100 km in combined city-highway driving, helping the Precept approach its target of 2.94 l/100 km. An ingenious multi-purpose unit handles regenerative braking through the rear wheels in addition to performing five other functions: it contributes 10 kW 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.
Architecture: Lightweight and Ultra-Efficient
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.
Since the weight carried by the front tires has been significantly reduced, no power steering 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 low rolling-resistance radial tires. The Precept's aluminum wheels each weigh only 3.8 kg, distinguishing them as the world's lightest 16-inch wheels. The friction brakes for the Precept save even more weight. An advanced brake-by-wire system uses a small electrically powered hydraulic pump located in close proximity to each brake caliper.
Aerodynamics Record: World's Best Four-Door Drag Coefficient
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.
Interior: Attractive, Functional and Driver-Oriented
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. The ultra-light front seats consist of powder-coated steel and aluminum frames with a bare minimum of foam padding and trim materials. A 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. 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.
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