Variable cycle three-stroke engine
A Variable cycle three-stroke engine is a type of internal combustion engine, patented by Michael A. V. Ward, US patent 5454352 dated Oct 3, 1995. Although the engine runs on the four-stroke cycle, the cycle is completed in one revolution of the crankshaft, as in the Atkinson cycle engine. However, this is achieved by the use of an elliptical cam instead of the jointed linkage used in the Atkinson engine.The three stroke engine does not exist in reality but according to the patent this cycle can be termed as 3 stroke. In reality it is a 2 stroke engine. The term "three-stroke" indicates that, to quote from the patent, "total cycle displacement (of) the engine equals approximately three expansion ratios". Thermal engine wherein the firing of gases is provided by controlled ignition, by compression up to the self ignition temperature, by compression under controlled pressure comprising a head-cylinder, a cylinder and a crankcase of the same type as the two stroke engine
The aim of the invention is to improve the emissions characteristics and efficiency of the internal combustion engine by reducing throttling and pumping losses. The patent states: "Other methods of reducing pumping loss rely on variable valve timing, as in the Miller cycle...these are only partially successful because they still employ a full intake and compression stroke with the accompanying mechanical frictional losses". In the engine proposed by Ward, the intake stroke is physically shorter than the expansion stroke.
Summary of the patent
The abstract reads: "A virtual three-stroke engine with intake and compression strokes approximately one half of the power stroke of approximately 12 to one expansion ratio and with total firing cycle stroke lengths equal to approximately three expansion strokes to minimize engine throttling and frictional losses over the real world drive cycle and provide high torque from a one-to-one drive shaft RPM to engine firing cycle RPM provided by a cam type driver for controlling the piston motions and extracting the power from the piston".
- "Patent US5454352 - Variable cycle three-stroke engine - Google Patents". Google.com. Retrieved 2012-06-15.
- US patent 5454352
- US patent 5454352
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