at around five atmospheres when the exhaust valve opens. Because the stroke is limited to that of the compression, still some work could be extracted from the gas. Delaying the closing of the intake valve in the Miller cycle in effect shortens the compression stroke compared to the expansion stroke. This allows the gases to be expanded to atmospheric pressure, increasing the efficiency of the cycle. Supercharger losses The benefits of using positive-displacement superchargers come with a cost due to parasitic load. About 15 to 20% of the power generated by a supercharged engine is usually required to do the work of driving the supercharger, which compresses the intake charge (also known as boost). Major advantage/drawback The major advantage of the cycle is that the expansion ratio is greater than the compression ratio. By intercooling after the external supercharging, an opportunity exists to reduce NOx emissions for diesel, or knock for spark ignition engines. However, multiple tradeoffs on boosting system efficiency and friction (due to the larger displacement) need to be balanced for every application. Summary of the patent The overview given above may describe a modern version of the Miller cycle, but it differs in some respects from the 1957 patent. The patent describes "a new and improved method of operating a supercharged intercooled engine". The engine may be two-cycle or four-cycle and the fuel may be diesel, dual fuel, or gas. It is clear from the context that "gas" means gaseous fuel and not gasoline. The pressure-charger shown in the diagrams is a turbocharger, not a positive-displacement supercharger. The engine (whether four-stroke or two-stroke) has a conventional valve or port layout, but an additional "compression control valve" (CCV) is in the cylinder head. The servo mechanism, operated by inlet manifold pressure, controls the lift of the CCV during part of the compression stroke and releases air from the cylinder to the exhaust manifold. The CCV would have maximum lift at full load and minimum lift at no load. The effect is to produce an engine with a variable compression ratio. As inlet manifold pressure goes up (because of the action of the turbocharger) the effective compression ratio in the cylinder goes down (because of the increased lift of the CCV) and vice versa. This "will insure proper starting and ignition of the fuel at light loads". Atkinson-cycle engine A similar delayed valve-closing method is used in some modern