2000 GMC Precept

Unveiled in January of 2000, the GMC Precept was introduced at the Detroit Auto Show. Utilizing a 100 kw fuel cell, the Precept was able to achieve 108 miles per gallon equivalent, due to its lightweight aluminum body. The low-emission vehicle concept car was aimed at establishing U.S. leadership in the development of extremely fuel-efficient vehicles while retaining the features that make them both marketable and cost-efficient. The first vehicle to ever reach the goal of achieving fuel efficiency equivalent to 80 miles per gallon of gasoline in tests conducted in October of 2000, the GM Precept advanced technology concept vehicle was quite innovative.

The GMC Precept was introduced at the North American International Auto Show as part of the Partnership for a New Generation of Vehicles with the rest of the Big Three and the US Government. GM created both a fuel cell and a hybrid version of this car.

The Precept was a fuel car that gets more than 100 miles per gallon and leaves no pollution in the air. Operating on three engines, the front electric motor used a mixture of hydrogen and oxygen while air coming through vents on the left and ride sides of the rear fenders is mixed with hydrogen stored on board. The mixture is then passed through a thin filter that grabs electrons and stores them in a battery and results in the harnessed energy that powers the front wheels of the car.

The electric engine is placed beneath the front seats and is approximately 15 centimeters high and 0.6 meters wide along the length of the vehicle and running from the left door to the ride door. The GM Precept also features minimal emissions. The only emissions are water vapor and some heat, while no carbon-based elements are used at all.

The internal combustion engine is centered between the two rear wheels and runs on a mixture of air and low-sulfur diesel fuel. The lean-burn combustion engine uses the heat created from the piston's compression stroke to ignite the fuel-air mixture rather than requiring spark plugs. A 30-bit, 266 MHz PC processor controls which engines are needed in specific instances such as gearing down, acceleration, cruising, and idling.

The diesel engine shuts down during coasting and braking while the two electric motors act as generators and utilize braking energy to recharge the batteries. The regenerative braking system adds an impressive 15 mpg to the fuel economy equation, according to GM.

The Precept's less-than-mainstream body is also another fuel-efficient design as its 0.16 coefficient of drag saves 4 mpg. Ideal flow over the rear of the vehicle is encouraged by grille openings in the rear quarter panels and tail that promote airflow through the engine compartment. The success of the body streamlining is found in a Cd of one-half that of a standard midsize sedan. Yet another feature adopted to improve aerodynamics is the dash-mounted video screen than eliminates the need for drag-inducing rearview mirrors.

The GM Precept features a heat pump climate control system that provides AC even during battery-only operation. Thermal energy from the drive systems is shunted to the heat pump for additional warmth in cold weather. Though padding is kept to a minimum to conserve weight, the seating is very similar to the sedans of today.

According to GM, weight reduction is only a small part of improving fuel economy. The real advances are accrued from drivetrain efficiency. The GM Precept weighs about 1000 pounds lighter than the average midsize sedans and also features other fuel-saving features that include manual steering, ultra high-pressure tires, and the extensive use of aluminum and other lightweight metals throughout the car.

The newest challenge is to now make hybrid vehicles much more affordable to the average consumer. After years spent fine-tuning, companies like GM now must work with their lab techs and suppliers to make hybrid production more cost-efficient.

By Jessica Donaldson