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Green Car Congress: Concept: Honda RD Developing Variable Compression Ratio Engine with Dual Piston Mechanism
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In testing in an otherwise conventional production 2.0-liter, 4-cylinder engine, the dual piston mechanism was able to adjust the engine from a CR of 9.6 to 14.2 and back again. Combining the high compression ratio with the Atkinson cycle, the engineering team demonstrated a 7.4% improvement in fuel economy in operation over the Japanese 10-15 cycle.
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They realized the movement of the dual piston mechanism by inertia and external hydraulic pressure, with the result that...
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...in contrast to the complexity, size and power demands of earlier VCR concepts, [Honda engineer] Kato said, the new dual piston VCR could be installed without changing any of the major parts of the engine such as the engine block.
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- The ratios are set at "high" and "low", though, not a range between the two.
- The engine was durability tested to 1 million cycles.
- Honda sees an efficiency advantage to this approach vs. turbo/supercharging a smaller displacement engine.
- Details are available in an SAE paper on the subject, presented at the SAE 2009 World Congress