25 years of turbocharging

Posted on 09. Jul, 2001 by in 2000-2009

2001-07-09

25 years of turbocharging

The Saab 99 Turbo was the first Saab turbocharged model. The initial run of 100 cars of this model was produced in 1977, and these cars were driven mainly by Saab?s own engineers and test drivers, and also by a number of selected private persons.

When the model was launched for general sale as a 1978 model, the impressive 145 bhp from the 2.0-litre, four-cylinder engine of the Saab 99 Turbo had already become acclaimed. Calculations showed that a six-cylinder engine with equivalent performance would have been about 50 kg heavier, and its fuel consumption would have been 30 percent higher.

This introduction served as the launchpad for Saab’s development of turbocharging technology, and this work is still ongoing. Saab is now unveiling the Saab 9-3 Anniversary special edition – the latest production development of the turbo concept.

When the turbocharging concept was first launched on a commercial scale, the benefit it offered was the surge of power that was ?on tap? for the 10 ? 15 percent of the motoring time when it was actually needed. During the rest of the operating time, the engine has the same fuel economy as an engine without turbo. The turbo does away with the need for large displacement and many cylinders to achieve a high engine output for situations such as safe overtaking and high average speeds on long journeys, without the downside of continuously high fuel consumption.

The turbo concept became an immediate success and was quickly adopted by other car manufacturers. Back in 1979, the world?s carmakers had five turbocharged models in production, but the total gradually rose to 66 in 1984, 90 in 1987 and 93 in 1990.

Turbocharged cars were being made even before the first 100 Saab 99 Turbos were produced in 1977. Very short runs of the Chevrolet Corvair Monza, Oldsmobile Jetfire, BMW 2002 Turbo and Porsche 911 Turbo had been equipped with exhaust-gas driven turbochargers that followed the principle invented back in 1905 by the Swiss engineer Alfred J. Büchi.

Saab contributed to the development of turbocharging to meet the needs in everyday motoring by equipping the turbocharger with a wastegate. The wastegate controls the boost pressure delivered by the turbocharger, to make the engine behaviour suitable for everyday motoring.

Turbocharging also proved to be part of the solution to other problems facing the world?s carmakers. In the early 1980s, new production processes and growing economic pressure led to petrol quality changes. The margins of safety to pre-ignition or ? knocking? that could cause engine damage were reduced, while car engines were designed to delivery more power.

Saab counteracted the risk of knocking by introducing the Automatic Performance Control (APC) system that ? listens? to the engine and lowers the turbocharger boost pressure as soon as it detects harmful knocking. This system would not have been as effective without interaction with the turbocharger.

As predicted by Saab, turbocharging also proved to be one of the keys to reduced exhaust emissions. The turbocharger improves the engine efficiency by putting to use the excess energy in the exhaust gases to increase the amount of air flowing into the cylinders. This reduces the fuel consumption and also improves the combustion efficiency. A turbo engine is more ? clean-running? than a naturally aspirated engine, and thus needs less complicated and heavy equipment for exhaust emission control.

Commercial success leads to further development
Saab produced its 100 000th turbo car back in 1983, and every third Saab produced in that year was a turbo. And the turbo concept was being developed at an accelerating pace. Still in 1983, Saab unveiled a development of the turbo engine that included double overhead camshafts and four valves per cylinder. Four valves can pass more fuel/air mixture and more exhaust gases than two valves. The engine is more efficient, and the four-valve arrangement also makes it simpler to optimize the design of the combustion chambers to achieve better combustion and cleaner exhaust gases.

Another environmental benefit of turbocharging was that it assisted in lowering the engine sound level. The turbocharger turbine blades ? break up? the sound before the exhaust gases reach the silencers, which can thus be made simpler and lighter.

Computerized turbo power
Saab?s development of turbocharging technology also brought about other design features in engine technology. In 1985, Saab introduced the Saab Direct Ignition (DI) system consisting of a compact cartridge that contains all the components of the ignition system. The DI system is a fully computerized, capacitive ignition system that has no moving parts or cables, and that also has other refinements such as the burst of sparks that burns away any moisture on the spark plug electrodes if the engine should fail to start first time from cold.

Within the space of less than ten years, Saab unveiled a succession of engine developments based on turbocharging technology ? the APC system, four valves per cylinder for family car engines, and the Saab DI system. In the mid-1990s, Saab introduced the Ecopower umbrella concept for its range of engines. This was on the back of yet another new feature based on turbocharging technology ? the Saab Trionic system.

The Saab Trionic system is based on a microprocessor capable of carrying out two million calculations per second. The processor is programmed with the ideal operating conditions of the engine as the basic reference. The Saab Trionic system then controls the electronic fuel injection system, the ignition, the throttle setting and the boost pressure, so that the engine will always be running as close as possible to its ideal conditions.

The Saab Trionic system also analyses the combustion after every ignition by measuring the ionization in the cylinders. The measurement reveals whether the fuel/air mixture has been ignited and burned correctly. If not, the system adjusts the amount of fuel injected, the ignition timing and the turbocharger boost pressure.

Saab Variable Compression
In March 2000, Saab Automobile AB unveiled a major item of world news that emerged from the turbo concept ? the Saab Variable Compression (SVC) engine.

SVC is an engine concept that enables the engine fuel consumption to be radically reduced, but without impairing engine performance. The combination of smaller engine displacement, high boost pressure by means of a compressor, and a system for varying the compression ratio enables the SVC engine to use the energy in the fuel far more efficiently than today?s conventional automotive engines.

The mechanical compressor used for supercharging is engaged and disengaged by the engine management system. The compressor delivers a maximum boost pressure of 2.8 bar, which is higher than the turbo system used by Saab today. Saab engine designers decided on a compressor instead of a turbocharger because there is currently no turbocharger on the market capable of delivering the high boost pressure and having the fast response needed by the SVC engine.

By supercharging the engine ? which means forcing more air into it than it would be capable of drawing naturally ? more fuel can be injected and burned efficiently. The engine thus exerts a higher force during every piston stroke, which results in a higher torque and higher power.

This design offers greatly improved opportunities for combining high performance with low fuel consumption and low exhaust emissions. Compared to today?s conventional engines, the SVC concept enables the fuel consumption to be reduced by up to 30 percent under normal motoring conditions.

The ability of the SVC engine to use new fuels in the future is probably its most important feature, rather than its low fuel consumption. Due to the variable compression ratio, combined with supercharging and a high-capacity engine management system, the engine can run on practically any liquid fuel.

Turbodiesel with novel turbine technology
Turbocharging technology from Saab was applied to a new engine type when the company introduced its first diesel engine two years ago. The engine displacement is 2.2 litres, and turbocharging enables it to deliver 125 bhp. Turbocharging technology has now surged ahead in the new Saab 9-5 3.0 TiD. The turbocharged 3.0-litre V6 engine of the Saab 9-5 is one of the world?s most advanced diesel engines and has pushed forward the boundaries of environmental adaptation and performance.

The Saab 3.0 TiD is an entirely new turbodiesel with intercooler. The engine delivers an exceptionally high torque of 350 Nm at 1800 rpm and develops 176 bhp at 4000 rpm ? values that can match those of the upgraded 2.3-litre High Output Turbo (HOT) engine in the Saab 9-5 Aero.

25 years of development of the turbo concept at Saab from the early high-performance 8-valve engine have resulted in an entirely new range of turbocharged petrol and diesel engines matched to the preferences of many different motorist categories. Emerging engine concepts such as the SVC engine also demonstrate that supercharging and turbocharging will continue to be part of the answer to the new challenges facing engine designers.

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