Hyundai has filed a patent for a three-cylinder engine with some very interesting technology.

The patent application was filed on November 30, 2015 but was published on March 16, 2017. In it, the Korean automaker details a three-cylinder engine where two of the cylinders perform four-cycle combustion while the remaining cylinder is two-cycle combustion. Essentially it’s a combined-cycle combustion engine in hopes of improving fuel efficiency, among other things.

'However, since the three-cylinder engine has structural characteristics in which bores, strokes, and valve timings of the respective cylinders are equal to one another, the engine generates noise and vibration compared to typical four or more cylinder engines,' the patent application says. 'To resolve this, it is necessary to devise a design technique for three-cylinder engines in which a three-cylinder engine combines a four-cycle with a two-cycle. In addition, since engine performance (for example, power and torque) is deteriorated when this combined cycle engine is controlled, merchantable quality of the engine may be lowered.'

It appears Hyundai is looking to solve the deterioration by combining two- and four-cycle cylinders. Since the bore, stroke and valve timing of the two-cycle cylinder can differ from the four-cycle cylinder, the same power is generated in the two- and four-cycle cylinders, preventing engine performance from dropping when the three-cylinder engine is operated under the combined cycles. It also maintains the advantages of a three-cylinder engine, mainly its compact structure and high fuel efficiency.

Expect to see more three-cylinder engines being developed by automakers in the coming years. The new Ford Fiesta ST for example, uses a three-cylinder EcoBoost engine to generate 200 horsepower and 214 pound-feet of torque.
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