New Saab Engine Tech

Tue Apr 18 02:59:41 GMT 2000

Check this out...interesting concept!

Doug

 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 engine¥and the key to
 its high efficiency¥is 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 conditions¥stop 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
 chamber¥in 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 part¥ the crankcase¥consists 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 respons
 e 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
 achieve¥just as they were with turbocharging in the 1 970s¥was 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 engine¥a 1.4 liter
 in-line six¥ 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
 system¥developed 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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