Geneva -Saab unveiled a tilting-head, variable-compression engine at this year's annual Motor Show here-which the car maker claims delivers 30% better fuel economy with peak power comparable to a conventional engine having twice the displacement. Key to the Saab Variable Compression (SVC) engine is a cylinder head with integral cylinders (the monohead) which is pivoted at the crankcase relative to the lower portion, made up of the engine block, crankshaft, and pistons. The five-cylinder, 1.6(liter) displacement engine, a prototype and not a production configuration, produces 225 hp and 224 lb-ft of torque.
The tilting mechanism in the Saab Variable
Compression engine changes the slope of the upper 'monohead' by up to 4
degrees relative to the engine base, which increases combustion chamber
volume, lowering the compression ratio at high
Compression ratio is de-creased for high load conditions (i.e. acceleration)
by a hydraulic actuator that tilts the monohead up to 4°relative to the
crankcase. This increases combustion chamber volume, lowering the compression
ratio to avoid fuel pre-ignition (knocking). A rubber bellows seals the monohead
to the crankcase. Taking into account the engine speed, load, and fuel type, the
engine management system continuously varies the compression ratio between 14
and 8:1. Other vital features include using a basically small displacement
engine (with low pumping losses) and a mechanical supercharger. Saab engineers
chose to forgo their trademark exhaust-driven turbocharger in favor of a
mechanical compressor because of the quick response needed by the SVC engine
along with double the boost pressure (2.8 bar or 40 psi) compared to their
current production engines.
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