Abstract: This engine is substantially free from any vibration and noise, small in friction loss, improved in mechanical efficiency to a considerable extent, compact and lightweight, and applicable to a reciprocating piston engine. The engine comprises: curved cylinders each assuming a circular shape in cross section; curved pistons (1, 1a) each fitting and reciprocating within the cylinder; a rotor (2) carrying the pistons (1, 1a) to keep them in balance and to have them be rockable about the center of the rotor (2), wherein the rotor (2) is provided with connecting rods (6, 6a) to impart half a rocking power of the rotor (2) to each of crank shafts (10, 10a) each of which converts the half of the rocking power to a piece of torque on its axis of rotation; a gear mechanism for receiving the pieces of torque to combine them into an output power; and, an output shaft connected with the gear mechanism for receiving and out-putting the output power.

Abstract: A link mechanism for a reciprocating piston engine and the like is characterized in that: motions of a pair of cylinder-type pistons moving in opposite directions relative to each other are converted into an oscillating-type rotary motion through an oscillating arm provided with a right and a left portion, which portions are equal in mass and in turning radius of their oscillating-type rotary motions; and, the oscillating-type rotary motion is divided into two equal parts by connecting rod means and transmitted to the link mechanism in which the two equal parts of the oscillating-type rotary motion are converted into a rotary motion of a rotary shaft incorporated in the link mechanism.