The Power of Saab - car maker develops new engines

Automotive Industries, Nov, 2000 by John McCormick

With GM'S support, Saab is developing radical new low-emission engine strategies that could make the Swedish brand a powertrain leader.

After languishing through the 1990s, Saab Automobile AB may be ready for a revival. Since General Motors Corp. took over full control of the Swedish carmaker last January, the building blocks have been put in place to give Saab what it needs: more investment, stronger management, a new chief designer and, most importantly, a broader product range.

According to Saab's CEO Peter Augustsson, the company's worldwide sales should top 140,000 this year and reach 200,000 by 2005. That's double the level typically achieved during the last decade.

"We will be producing five to seven new products over the next five years," says Augustsson. Saab will rely heavily on GM'S new Epsilon platform as the basis for several of these new models.

From a styling perspective, Saab will continue to display distinctive visual cues, says new design director Michael Mauer, who joined the company from Mercedes-Benz where his credits include the Smart city car and the A-Class. "But I would like to see more of a revolution than an evolution in Saab design as we go forward," asserts Mauer. "The current products are too mainstream." Under Mauer's guidance, the Saab advanced design center in Trollhattan is starting work on the company's first concept car in many years.

In terms of engineering, Saab has been designated the center of expertise for "overcharged" engine development within the GM empire. This is hardly a surprising move, considering Saab's long experience with turbocharging technology. Beyond developments in high- and low-pressure turbocharging, Saab engineers have been working on two radical new engine combustion strategies. One is a variable-compression concept, first reported by Automotive Industries in the April 2000 issue (see page 19). The second concept is dubbed Saab Combustion Control (SCC). Both programs are aimed at reducing emissions and increasing efficiency. The story below provides an update on each program, including a first-drive impression of cars equipped with the SVC powerplant.

SCC: Approved for Production

Saab's Combustion Control (SCC) is an attainable technology with a solid production future. According to Eric Olofsson, Saab's powertrain combustion manager, the system will be featured in the next generation 9-3 and 9-5 models due in two or three years.

The impetus for SCC are tighter exhaust emission standards planned for the U.S. and Europe by 2005. The upcoming U.S. federal Tier 2 and more stringent California standards focus on limiting nitrogen oxide (NOx) and hydrocarbon (HC) emissions, while the European Euro IV regs put greater emphasis on reducing carbon dioxide ([CO.sub.2]) emissions.

Saab engineers claim SCC achieves this goal while simultaneously lowering fuel consumption by up to 10 percent -- and without reducing engine performance. They say SCC exhaust emissions will comply with the California Ultra Low Emission Vehicle 2 (ULEV2) requirements set to take effect in 2005. Compared to Saab engines with equivalent performance today, this will reduce the carbon monoxide (CO) and HC emissions by almost half and will cut NOx emissions by 75 percent.

The secret to SCC is a combination of four key features: air-assisted direct fuel injection developed jointly with Orbital Engine Corp., featuring a novel spark plug injector from Delphi-Orbital; variable valve timing; a variable spark gap; and special piston-crown geometry.

Orbital's direct fuel injection process, which the Australian company says is being evaluated by 10 other OEMs, uses low-pressure air to inject a finely atomized fuel spray directly into the cylinder. This contrasts with competing lean burn high-pressure direct injection systems which require a catalytic converter with a NOx trap to control emissions. Such catalysts are costly and require low-sulfur fuel for proper operation.

In the SCC system, the injector unit and spark plug are integrated into a spark plug injector (SPI). The fuel is injected directly into the cylinder by means of compressed air. Immediately before the fuel is ignited in low torque conditions, a second brief blast of air creates turbulence in the cylinder, which facilitates combustion and shortens the combustion time.

Both the inlet and exhaust camshafts have steplessly varied timing, which allows exhaust gases to be recirculated into the combustion air. This maintains the ideal near-stoichiometric fuel/air mixture (14.6:1) under almost all operating conditions. In low torque conditions, the exhaust gases compose up to 70 percent of the cylinder's volume during combustion. The exact proportion depends on the prevailing operating conditions with the proportion of exhaust gas to ambient air decreasing as the torque demand increases.

The variable-spark-gap element in the SCC system is actually a further development of the spark-to-piston concept Saab unveiled at the 1995 Frankfurt show. The spark plug gap is variable between 1.0 and 3.5 mm. A central electrode in the spark plug injector strikes a spark to either a fixed-ground electrode 3.5 mm away (in low torque) or to a grounded electrode on the piston (under high torque). The variable spark gap, together with a high spark firing energy (80 mJ), is essential for igniting an air/fuel mixture that may have a high percentage of exhaust gases.