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Message: <blockquote data-quote="RJ_5847" data-source="post: 1458909" data-attributes="member: 32521">yep true...Variable Compression Ratio - Saab SVCSaab has stunned the world by showing its variable compression ratio engine in the 2000 Geneva motor show. I’ve heard such engine for some 2 years, but this is the first time Saab disclose the details to the press. In my opinion, this is perhaps the largest single breakthrough in engine technology since turbocharging and electronic engine management. Why is variable compression ratio so fascinating? As everybody knows, fixed compression ratio is always a constraint for supercharging or turbocharging engines. To prevent excessive pressure in combustion chamber, hence pre-ignite ("knocking") and overheat to cylinder head, turbo/supercharger engines always employ a much lower compression ratio than normally aspirated engines so that the total pressure won’t exceed the limit when the boost pressure is added. The problem is, when the charger (especially is turbocharger) is not yet getting into full boost, that is, at low and mid rev, the combustion runs at lower compression ratio than normally aspirated engines. Therefore power efficiency at low speed is even lower than normally aspirated engines. As seen, the SVC engine have a cylinder head with integrated cylinders - which is known as monohead. The monohead is pivoted at the crankcase and its slope can be adjusted slightly (up to 4 degrees) in relation to the engine block, pistons, crankcase etc. by means of a hydraulic actuator, therefore the volume of the combustion chamber (when piston is in compressed position) can be varied. In other words, compression ratio is also variable. SVC is cleverer than any previous patents for variable compression ratio engines is that it involves no additional moving parts at the critical combustion chamber or any reciprocating components, so it is simple, durable and free of leakage. The monohead is self-contained, that means it has its own cooling system. Cooling passages across the head and the cylinder wall. There is a rubber sealing between the monohead and engine block. The VC allows the Saab engine to run on very high supercharging pressure - 2.8 bar, compare with the latest 911 turbo’s 1.94 bar, or about twice the boost pressure using by 9-3 Viggen. So high that today’s turbochargers cannot provide. Therefore it employs supercharger instead. At other speed, the VC is adjustable continuously according to needs - depends on rev, load, temperature, fuel used etc., all decided by engine management system. Therefore power and fuel consumption (hence emission) can be optimized at any conditions.</blockquote>

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