Engine with rack gear-type piston rod

An engine with a rack gear-type piston rod, comprising:

• first and second cylinders disposed oppositely to each other along a first common axis, the cylinders respectively having first and second pistons that move back and forth along the first common axis;
• third and fourth cylinders disposed opposite to each other along a second common axis, the third and fourth cylinders respectively having third and fourth pistons that move back and forth along the second common axis;
• a first piston rod, for connecting the first piston to the second piston, that is provided with upper and lower gear teeth formed on its opposing faces for enabling back and forth motion that responds to the back and forth motion of the first and second pistons;
• a second piston rod, for connecting the third piston to the fourth piston, that is provided with upper and lower gear teeth formed on its opposing faces enabling back and forth motion that responds to the back and forth motion of the third and fourth pistons with a phase difference of 180 degrees;
• a first gear train including at least three gears engaging the upper and lower portions of the first and second piston rods;
• the three gears rotating in opposite directions in response to the back and forth motion of the piston rods;
• one way clutches mounted on one sides of the three gears, respectively;
• a second gear train including at least three middle gears each connected respectively to one of the one way clutches through the respective middle shaft and idle gears engaged between the middle gears;
• and
• an output gear connected to one of the middle gears of the second gear train.