The Shape Of Tomorrow.

GM's Precept proves that creating an 80-mpg, five-passenger sedan is needed rocket science.

The vehicle you're looking at is probably the closet any automaker has come to creating the theoretical equivalent of a Saturn V booster rocket, Apollo capsule and lunar lander, all in one car.

At least that's what the innumerable bytes of data, collected during simulation and subsystem testing, indicate the car can do. Program boss Dr. Ron York, GM's PNGV director, is "extremely encouraged" by dyno tests so far. He says he hopes to know for sure next, month that the Precept has hit its main bogey.

Precept development was certainly driven with space-shot levels of intensity and sense of purpose. And like the Apollo project, it didn't enjoy one big breakthrough. "This vehicle is not a home run," offers York, a former aerospace engineer. "Rather, it represents hundreds of singles, hit over a 3 1/2-year development span."

To achieve its amazing fuel economy, the car's energy demands had to be reduced by half, compared with today's most efficient production vehicles. By GM calculations, that meant reducing mass by 40 percent; reducing aerodynamic loads by another 33 percent; cutting rolling resistance by another 33 percent, and lowering accessory loads by half.

At the same time, propulsion system efficiency had to rise by 50 percent. That required a 40-percent boost in engine thermal efficiency, York notes, and a one-third reduction in driveline losses.

"We eventually adopted two mottos: Yes, we must reinvent the wheel, and yes, this is rocket science!," he recalls.

The Precept and its Ford and Daimler-Chrysler counterparts are the proof-of-concept vehicles called for by the Partnership for a New Generation of Vehicles, the joint program launched in 1993 between the former Big Three automakers and the U.S. government. PNGV's primary goal is to use collaborative R&D, flexing the techno-muscles of U.S. research labs and the industry, to help each automaker develop an ultra efficient, five-passenger sedan. The cars must be capable of delivering at least three times the fuel economy of today's Taurus, Lumina and Intrepid. That equals 80 mpg with gasoline engines, and 90 mpg with advanced diesels. These cars also must meet all regulatory and customer requirements, and be affordable.

The PNGV program, which after some political wrangling allowed the newly Germanized Chrysler to participate, set an aggressive timetable. Proof-of-concept vehicles are due this year, with production prototypes following by 2004. Only GM and Ford had their concepts ready to unveil at this month's Detroit auto show (see p. 26). GM was the first to give reporters background on its program last October, and AI was the first publication to see the actual vehicle a month later.

"PNGV is about developing vehicles as a system, which is how the greatest efficiency gains are made," observes Ken Baker, CEO and director of the Environmental Research Institute of Michigan, an Ann Arbor-based non-profit scientific research firm. Baker retired from GM last February as vice president of R&D. He believes the Precept and its PNGV counterparts will help the industry "take a quantum leap forward in improving the production feasibility, including lowering cost, of many new technologies."

Such progress will be necessary, as the auto industry faces tougher emissions and fuel economy pressures in the years to come. "The status quo is no longer acceptable," says environmental policy consultant James Cole, of Cole & Assoc. in Fenton, Mich. "Regulators will never again let a standard sit for 20 years, because the public won't tolerate it."

Cole adds that the key to the Precept and the others' success "will be how quickly the companies adapt these ultra-efficient drive-trains and technologies to light truck and SUV platforms."

At its peak, GM's Precept effort involved 200 people, including specialists from GM R&D, stylists from Design Center and supplier experts. Leading development was the Advanced Vehicle Team (AVT), GMs talented group located in Troy, Mich., that's charged with making advanced technologies production ready. Many of them had worked on the EV1 electric car 10 years ago. York and ERIM's Baker agree that the EV1 has served as a "knowledge platform," paying big dividends in aerodynamics, lightweight materials, battery development and power control architecture. "The most important investment GM made on EV1 was the team structure," says Baker. "Now it's paying off as they develop Precept."

The body exterior team alone spent nine months and 160 hours in the wind tunnel, honing one-third and full-scale models toward their drag coefficient target of 0.18 Cd. The car's final shape was even slicker. 0.163 Cd. Even before the physical form was created, ATV's computational fluid dynamics and advanced modeling software indicated that the digital design was within 10 percent of the aero target. The 0.163 number makes the Precept the world's most aerodynamic passenger vehicle.

For AVT, it was the ultimate in synergistic vehicle development. "We had to tackle every point on the car," admits director Bob Purcell. The project spawned over 130 recognized innovations, many of which he promises "will be translated into `real hardware' for GM's core vehicles."

After more than a year of evaluating driveline strategies, the ATV team in summer 1997 decided on a parallel hybrid system with all-wheel drive. In a parallel hybrid, the internal-combustion engine and transmission are coupled to an electric motor/generator, with a continuing link to the drive wheels. The objective with multiple power sources is that each keeps the other operating close to its maximum efficiency (steady-state rpm, in the case of the engine). AVT chose all-wheel drive to allow four-wheel regenerative braking -- "a key to our efficiency goals," notes York. Under deceleration or braking, unwanted vehicle momentum is automatically converted to electricity that's used to charge the car's nickel-metal hydride (NiMH) battery pack, supplied by Ovonic. The Precepts engineers claim the four-wheel regen is good for 13 mpg in combined city/highway driving, compared to a car without regen braking

Lithium-polymer and lithium-ion battery strategies are also being developed. And the Precept ultimately will be fitted with GM's latest fuel cell power system

But for now, GM claims the Precept's front and rear drive systems, with the engine at wide-open throttle, can accelerate the 2,650-pound car to 60 mph in 12 seconds.

Electrical power control is essential to hybrids and future vehicles in general. The Precept's brainpower comes from an all-new Motorola 32-bit, 266 MHz processor. It manages the car's advanced electrics, which are bused in multiple (12V, 24V and 42V) voltages. Some of the supplies are staged, with power delivered according to load. The vehicle has four central controllers (central body, energy management, climate/thermal and hybrid drive system), along with 18 distributed nodes. There are 28 total microprocessors on board.

Lighting is entirely by LED, which is far more efficient than incandescents (see lighting story, p. 33). The hybrid system is set up to power the HVAC either with the engine or the multipurpose unit. For cold weather, a heat pump augments the cabin heater, as the little turbodiesel doesn't offer much waste heat.

Once the basic hybrid power system was established, the team then looked at where to put the engine to best maximize the car's extreme aerodynamic goals.

"Our thinking was out-of-the-box," recalls Bill Shepard, the staff development engineer in charge of the Precept's packaging. "We decided the best place to put the engine is in the rear. This eliminated plumbing and allowed us to close off the car's front end, for much improved frontal aero."

Adds colleague Mike Kutcher, engineering group manager at ATV, "We knew that to improve on the EV1's 0.19 Cd, we had to go to a non-front-breather. That meant a rear engine layout. It was a huge enabler, helping us to go 30 counts of drag (0.030) beyond EV1 with this car."

With the rear engine configuration, the Precept's huge heat exchangers are mounted vertically, flush with the rear quarter panels and fed by ram-effect inlets above each rear wheel. Cooling fans aid airflow into the engine compartment. Eliminating the radiators from the front of the car allowed the hood line to be lowered further.

The resulting design controls turbulence over the rear of the car. And air that flows through the heat exchangers is exhausted (via the mar fascia grille) into the wake area behind the car, which helps reduce drag by "making the body think it's tapered, like EV1," Kutcher says. More than 80 hours of wind tunnel time was spent on mar thermal system issues.

The other two main aero enablers are a flush, smooth underbody and the replacement of conventional exterior mirrors with a camera system It alone is worth a 17 percent reduction in drag.

Clever design and engineering are everywhere on this vehicle. Clearly the Precept pushes the efficiency envelope farther than Honda's Insight and Toyota's Prius, although the Japanese cars are already in production (see Dec. '99 AI, p.28). ATV has shown the world how to achieve + 80 mpg in a five-passenger sedan. Now it's GM's job to transfer this inventiveness into the real world.

RELATED ARTICLE: Tatra Paved The Way

While GM's amazing Precept may be a preview of future passenger cars, its general configuration is over 60 years old. Even before designer Alex Tremulis was finishing Preston Tuckers ill-fated Torpedo in 1947, a European automaker had been building roomy, streamlined, rear-engined cars for over a decade.

Czechoslovakia's Tatra cars of the 1930s through the 1960s are Precepts spiritual forefathers. Tatra's chief engineer, Hans Ledwinka, believed that rear-mounted air-cooled engines gave the best package efficiency and body streamlining opportunities. Beginning with the T12, a small car produced in 1923 that strongly influenced Ferdinand Porsche's design of the VW Beetle, Ledwinka progressed to innovative T87 sedan of the late 1930s (see photos at left and below).

The fastback T87's inspired aerodynamic cues included a dorsal stabilizing fin that extended from the roof, down the back of the car. Equally unique was a 3.0L sohc, air-cooled V-8 mounted behind the rear axle. The car also wore three head-lamps, making it far more attractive from the rear than from the front

In 1946, the Czech Communist government nationalized Tatra and threw Ledwinka into prison, a scapegoat for his company's support of the Nazis during World War II. His successor, Julius Mackerle, continued to evolve the air-cooled, rear-engine layout in a variety of models, ending with the T603 large sedans launched in 1957 and built through the mid-1960s.

Although the Tatra bodies were not aimed at maximum aerodynamics, they were designed to manage dynamic air pressure over their rear ends, where engine intake, cooling and heat rejection were most critical. Like Precept, large intake and cooling ducts were located first on the sail panels (see photos), and later on the rear fenders. Belt-driven axial fans mounted under each cylinder bank pulled in cooling air. Heated air was exhausted through the car's rear bumper, via a thermostat-controlled flap.

Today, Tatra specializes in heavy trucks. But its passenger car past showed the way for tomorrow's high-efficiency vehicles.

--LB

RELATED ARTICLE: And Ford Unveils Its Prodigy

Ford admittedly took a simpler, less radical route to PNGV than GMs (see p. 17), but the result is no less impressive. Ford PNGV boss Vince Fazio claims the handsome Prodigy can achieve "better than 70 mpg" from its 1.2L turbodiesel-electric hybrid drivetrain, and 0.199 Cd. The aluminum-intensive car weighs just 2,387 pounds and benefits from many of the same aero features as the Precept, including rear-vision cameras, variable ride height and full belly pan. Prodigy's a "front breather," but grille opening has louvers that automatically open only when needed. The hybrid-drive system is based on a 35 kW starter-alternator and Varta "low storage" 4 amp/hour, NiMH battery pack, Regen braking is off the two front drive wheels. Claimed zero-to-60 mph acceleration is 12 seconds, same as the Precept.