Patent ID: 7273028

Claim:
In an engine having a crankshaft, a piston connected to said crankshaft by a connecting rod, a counterweight coupled to an end of said connecting rod, two bearings arranged on said crankshaft on two opposite sides of said counterweight, a drive gear arranged between said counterweight and one of said bearings, a balance shaft arranged on one side and spaced from said crankshaft and extending in a direction parallel to a rotational axis of said crankshaft, the improvement wherein said balance gear system is mounted on said balance shaft and is engaged with said drive gear, said balance gear system comprising a primary gear, a secondary gear, a torsional spring and a limiting pin, said primary gear having a securing hole, a first insertion hole, and a first central bore around which a circumferential circular flange is formed, said second gear having a through hole, a second insertion hole, and a second central bore, said securing hole, said first insertion hole and said first central bore of said primary gear being aligned with said through hole, said second insertion hole, and said second central bore of said secondary gear respectively, said torsional spring being formed with a first and a second U-shaped ends, said first U-shaped end being fit into said first insertion hole, said second U-shaped end being fit into said second insertion hole, said limiting pin having a head section and a stem section extending from said head section and having a diameter smaller than a diameter of said head section, said head section of said limiting pin being fit into said through hole of said secondary gear, said diameter of said head section being smaller than a diameter of said through hole of said secondary gear thereby forming a gap between said head section of said limiting pin and said through hole of said secondary gear, said secondary gear being coupled to said primary gear by fitting said second central bore of said secondary gear over said circumferential circular flange of said primary gear to having said primary and secondary gears engaging each other in a face-to-face manner, said secondary gear being fit over said circumferential circular flange of said primary gear in a sliding fit manner thereby allowing said secondary gear to be rotatable about said circumferential circular flange of said primary gear, said central bore of said primary gear being fitted over said balance shaft in a tight-fitting manner with said secondary gear abutting against a circumferential shoulder formed on said balance shaft, said balance shaft being arranged to mate both said primary and secondary gears with said drive gear thereby causing said balance shaft to be rotated in unison with said crankshaft.