SAAB REVEALS UNIQUE ENGINE CONCEPT THAT OFFERS HIGH PERFORMANCE AND LOW
FUEL CONSUMPTION

Press photos available at: http://www.saabnet.com/tsn/press/


At the Geneva Motor Show, Saab Automobile AB unveils the Saab Variable
Compression (SVC) engine, a new engine concept that enables fuel
consumption to be radically cut while increasing engine performance per
liter of engine displacement. The combination of reduced engine
displacement, high supercharging pressure and a unique system for varying
the compression ratio enables the SVC engine to use energy in fuel far more
efficiently than today's conventional automotive engines. SVC offers an
entirely new concept for combining high performance with low fuel
consumption and low exhaust emissions.

Fuel consumption 30 percent lower

The SVC concept reduces the fuel consumption of a conventional naturally
aspirated engine by up to 30 percent while at the same time providing
impressive performance. The five-cylinder SVC engine developed by Saab has
a displacement of 1.6 liters and is as fuel-efficient under normal
conditions as a conventional 1 .6-liter engine, but can deliver power
comparable to a highly tuned 3.0-liter engine when needed. The carbon
dioxide (CO2) emissions are reduced proportionately to the fuel
consumption, while the CO, HC and NOx emissions will enable the SVC englne
to meet all current and proposed future emissions regulations. The unique
feature of the SVC engineÑand the key to its high efficiencyÑis that the
engine has a variable compression ratio. The fixed compression ratio of a
conventional engine is a compromise between a wide variety of operating
conditionsÑstop and go city traffic, highway motoring at constant speed, or
high-speed freeway driving. The compression ratio of the SVC engine is
continually adjusted to provide the optimum value for varying driving
conditions.

Variable combustion chamber volume for variable compression ratio

The SVC engine is comprised of a cylinder head with integrated cylinders,
which is known as the monohead, and a lower portion consisting of the
engine block, crankshaft and pistons. The compression ratio is varied by
adjusting the slope of the monohead in relation to the engine block and
internal reciprocating components. This alters the volume of the combustion
chamber with the piston at top dead center (highest position of the piston
in the cylinder), which, in turn, changes the compression ratio.

The combination of reduced engine displacement, high supercharging pressure
and a variable compression ratio enables the SVC concept to provide engines
with tremendous power output capabilities. The 1.6 liter, 5-cylinderengine
produces 147 Ib.-ft. oftorque and 150 horsepower per liter of engine
displacement! The SVC concept opens the door to the development of both
small, extremely fuel-efficient engines with good performance, and larger
engines delivering sports car performance with high fuel-efficiency.

Alternative fuels

The variable compression ratio also gives the engine excellent fuel
flexibility. Since the compression ratio can be varied and adjusted to suit
the properties of fuel, the engine will always run at the compression ratio
that is best suited to the fuel being used.

Three cornerstones of the SVC concept

Although a vanable compression ratio is what makes the SVC engine unique,
the fuel efficiency of a conventional naturally aspirated engine would only
improve 4 - 5 percent if it were equipped with a variable compression
system. The full potential of variable compression can only be realized
when it's used in combination with reduced engine displacement and high
supercharging pressure.

1. Reducing the enaine dispIacement- size does matter

A conventional four-stroke gasoline engine is most efficient (maximizing
the energy in the fuel) when it is running at a high load. A small engine
must work harder and run closer to full load if it is to perform the same
work as a bigger engine, which utilizes only part of its maximum capacity.
The small engine often extracts more energy from every drop of fuel.

One reason for this is because the pumping losses are lower in a small
engine. Pumping losses arise when the engine is running at low load and
when its fuel consumption is relatively low. In order to maintain the ideal
air-to-fuel ratio (14.7:1), the air supply must be restricted by reducing
the opening of the butterfly valve in the air intake.

However, this means that the piston in the cylinder is under a slight
vacuum during the suction stroke, when it is drawing air into the cylinder.
The effect is roughly the same when you cover the air hole of a bicycle
tire pump with your thumb while trying to pull out the pump handle. The
extra energy needed for pulling the piston down is known as the pumping
loss. Since a small engine frequently runs at full load and the throttle is
therefore more often fully open, the pumping losses in the small engine are
usually lower than they are in a big engine.

Additionally, a small engine is lighter, has lighter internal reciprocating
mass and has lower frictional losses. Therefore, a small engine is
generally more efficient than a big engine.

2. Supercharging - Power on tap

Although a small engine is efficient, it is not powerful enough to be used
for anything other than powering small, lightweight cars. By supercharging
the intake air and forcing more air into the engine, more fuel can be
injected and bumed efficiently. The engine then delivers more power for
every piston stroke, which results in higher torque and horsepower output.
By supercharging the engine only at greater throttle openings when extra
power is really needed, the fuel economy of a small englne can be combined
with the greater performance of a big engine.

Small displacement engines and supercharging have long been well-known
concepts at Saab. Saab launched the turbo concept back in 1976 as a way of
boosting the performance of an engine by raising the intake air pressure,
but without making the engine bigger and heavier, and therefore less fuel
efficient.

Over the last 25 years, Saab has developed a number of innovative
turbo-enhanced engine systems, all of which have resulted in boosting
performance, lowering fuel consumption and reducing exhaust emissions.
However, engine development has now reached the stage at which a new
parameter of the combustion process must be optimized to meet future
demands for reducing the carbon dioxide emissions and enabling alternative
fuels to be used. Varying the compression ratio is the ideal parameter to
optimize.

3.Variable compression - pearl of wisdom

The compression ratio of an engine is the piston displacement volume plus
the volume of the combustion chamber divided by the volume of the
combustion chamberÑin other words, the amount by which the fuel/air mixture
is compressed in the cylinder before it is ignited. The compression ratio
is one of the most important factors that determine how efficiently the
engine can utilize the energy in the fuel.

The energy in the fuel will be better utilized if the compression ratio is
as high as possible. But if the compression ratio is too high, the fuel
will pre-ignite, causing 'knocking,' which could damage the engine. In a
conventional engine, the maximum compression ratio that the engine can
withstand is therefore set by the conditions in the cylinder at high load,
when the fuel and air consumptions are at maximum levels. The compression
ratio remains the same when the engine is running at low load, such as when
the car is travelling on the highway at constant speed.

Due to its variable compression ratio, the SVC engine can be run at the
optimum compression ratio of 14:1 at low load in order to maximize the use
of the energy in the fuel, and the compression ratio can then be lowered to
8:1 at high load to enable the engine performance to be enhanced by
supercharging without inducing 'knocking.'

New ways of using known engine components

An objective in the development of the SVC concept was to retain as many of
the basic components of a conventional engine as possible. The crankshaft,
connecting rods, pistons and valves are all of the same type as those of
today's engines. What distinguishes the SVC engine is the way it is split
into upper and lower portions. Compared to a conventional engine, the joint
face between the two is about 20 centimeters (almost eight inches) lower.
The upper part, known as the monohead, consists of the cylinder head with
integrated cylinders, whereas the lower partÑ the crankcaseÑconsists of the
engine block, crankshaft, connecting rods and pistons.

The monohead is pivoted at the crankcase. The compression ratio is altered
by tilting the monohead in relation to the crankcase by means of a
hydraulic actuator. The volume of the combustion chamber will then increase
and therefore lower the compression.

To increase the compression, the slope of the monohead is reduced. The
volume of the combustion chamber will then decrease and the compression
will be higher. The monohead is sealed at the crankcase by a rubber
bellows.

The monohead can be sloped by up to 4 degrees. The optimum compression
ratio is calculated by the Saab Trionic engine management system based on
the engine's speed, engine load and fuel quality. The compression ratio is
continuously variable.

Efficient four-valve combustion chambers

An important benefit of the SVC concept is that the variable compression
can be achieved without modifying the design of the efficient four-valve
combustion chamber. The combustion chamber design is of vital importance to
the combustion process, and therefore directly affects the exhaust
emissions, fuel consumption and engine performance. One of the essential
conditions in the work of developing the SVC concept was that the new
technique should not impair the existing design.

Since the monohead is made as one unit, it is also possible to enhance the
design of the coolant passages. This is essential for being able to
supercharge the engine sufficiently to achieve high performance.

Mechanical compressor for maximum boost pressure and fast response

The mechanical compressor used for supercharging is engaged and disengaged
by the Saab Trionic engine management system. The compressor is equipped
with an intercooler and delivers a maximum boost pressure of 2.8 bar (40
psi), which is double the boost pressure delivered by today's Saab 9-3
Viggen and 9-5 Aero high output turbo engines. Saab engine designers chose
to use a compressor instead of a turbocharger for the SVC engine because
today's turbochargers are not able to deliver the high boost pressure and
fast response needed by the SVC engine.

A plafform for continued development

The SVC concept and the 1.6-liter, five-cylinder engine represent a leap
forward in engine technology and provide a completely new plafform for
further engine development. The fact that the compression ratio parameter
can now be controlled enables more accurate engine operation, and
therefore, higher efficiency. SVC can be combined with other engine
technologies to further improve performance, lower fuel consumption and
reduce exhaust emissions.

The SVC engine represents a decisive step in the long-term development work
aimed at combining the benefits of the Otto engine and the diesel engine.
This trend is already visible in engine development. Direct injection will
be used on the Otto engine just as it is on the diesel engine, while the
diesel engine will have much more electronics. Variable compression has
thus far been the missing link between the two.

Engine innovators

The importance of the compression ratio to the efficiency of an engine has
long been known, and there are many imaginative patents for different
designs of variable compression engines. What Saab engine designers were
first to achieveÑjust as they were with turbocharging in the 1 970sÑwas to
combine innovative new thinking with a known technique and proven theories
in order to develop a system that is usable.

Saab engine designers began thinking about developing a variable
compression engine in the early 1 980s, but it was not until the end of the
1 980s that more concrete development work was started, albeit on a modest
scale. The first patent application was lodged in 1990. The first usable
experimental engine had a displacement of 2.0 liters, and delivered higher
torque and power output than was necessary. But the engine did prove that
the theory performed well.

Actual testing began when the second generation prototype engineÑa 1.4
liter in-line sixÑ was ready in the mid-1 990s. The objective was that an
SVC engine of that design would have the performance and power output of a
naturally aspirated 3.0-liter V6 engine, but with 30 percent lower fuel
consumption. In order to have the potential of the SVC engine assessed by

independent experts, Saab approached the renowned German engine development
company FEV Motorentechnik in Aachen. They submitted a thorough evaluation
to confirm that the engine met the desired targets, and that it was also
possible to make further advances by continued development work.

However, the six-cylinder, 1.4-liter in-line engine was not appropriate to
the performance level needed by the projected Saab range of cars. The
engine also entailed packaging disadvantages. So it was dropped in favor of
the current five-cylinder, 1 .6-liter engine concept.

The SVC concept would have been impossible to develop without an advanced
engine management system. The addition of variable compression as another
control parameter in the already complex control system of today's
automotive engines creates high demands on the engine management system.
The engine management system for the SVC engine is a special version of the
Saab Trionic systemÑdeveloped in-house by Saab and in use on Saab
turbocharged engines since 1991. Further development of the Saab Trionic
system and the in- depth knowledge of the system accumulated by Saab
engineers have been key elements in the development of the SVC concept.

However, even in its latest version, the Saab five-cylinder, 1 .6-liter SVC
engine is still at the prototype stage and further development work is
needed before the engine can be used in regular production. The final
design and size, and also the performance and fuel consumption properties
of the ultimate production engine are dependent on many factors, including
meeting the future demands of customers.

Technical data

The figures below relate to the 1 .6-liter test engines currently used in
Saab's ongoing technical development work. The exact technical
specifications of future regular production engines will be dependent on
this development work, future customer demands for performance and fuel-
efficiency and Saab's overall product plans.

Engine displacement     1.598 liter
Number of cylinders     5
Cylinder bore           68 mm
Piston stroke           88 mm
Compression ratio       8:1 to 14:1, depending on engine load
Max. compressor boost pressure 2.8 bar (40 psi)
Max. monohead tilt angle       4 degrees
Peak engine torque           224 Ib.-ft.
Engine rating           225 hp
==================
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• Press: Saab Variable Compression (SVC) Engine, The Saab Network, Sat, 18 Mar 2000 09:50:13

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