An engine balance shaft (20) for an internal combustion engine (24) is provided having reduced total mass and rotational inertia while having sufficient bending stiffness and sufficient unbalance mass. The balance shaft (20) is formed by fixedly coupling a counterweight (56), a front bearing journal (68), a rear bearing journal (60), a tail piece (40), and a nose piece (44) to a hollow tube (52). The hollow tube (52) is hydroformed to expand the diameter of the tube and fasten the desired components to the tube (52).

An internal combustion engine includes: a wall body that is formed on a crankcase to accommodate a generator by sandwiching the generator between the wall body and a generator cover coupled to the crankcase from outside; a casing that includes a casing wall, the casing wall being formed on the crankcase and, at a position apart from the wall body in an axial direction of the crankshaft, facing the wall body with a space contiguous to an outer surface of the crankcase sandwiched between the casing wall and the wall body; and a balancer shaft that has an axis thereof parallel to the rotation axis of the crankshaft, and is rotatably supported by the casing while one end of the balancer shaft protrudes from the casing wall into the space. Accordingly, the engine can reduce its weight by shortening the balancer shaft as much as possible without upsetting weight balance.

An internal combustion engine includes: a wall body that is formed on a crankcase to accommodate a generator by sandwiching the generator between the wall body and a generator cover coupled to the crankcase from outside; a casing that includes a casing wall, the casing wall being formed on the crankcase and, at a position apart from the wall body in an axial direction of the crankshaft, facing the wall body with a space contiguous to an outer surface of the crankcase sandwiched between the casing wall and the wall body; and a balancer shaft that has an axis thereof parallel to the rotation axis of the crankshaft, and is rotatably supported by the casing while one end of the balancer shaft protrudes from the casing wall into the space. Accordingly, the engine can reduce its weight by shortening the balancer shaft as much as possible without upsetting weight balance.

An internal combustion engine includes: three or more cylinders including cylinders A, B and C according to the present disclosure arranged in a row in the cylinder row direction; and a balancer device for reducing engine vibration. The balancer device includes a balancer shaft arranged so as to extend from the cylinder A to the cylinder C along the cylinder row direction in a crank chamber. The balancer shaft includes: a first opening formed on the outer surface of the balancer shaft at a first location associated with the cylinder A in the cylinder row direction; a second opening formed on the outer surface at a second location associated with the cylinder C in the cylinder row direction; and a communication passage formed inside the balancer shaft so as to connect the first opening with the second opening.

An internal combustion engine includes: three or more cylinders including cylinders A, B and C according to the present disclosure arranged in a row in the cylinder row direction; and a balancer device for reducing engine vibration. The balancer device includes a balancer shaft arranged so as to extend from the cylinder A to the cylinder C along the cylinder row direction in a crank chamber. The balancer shaft includes: a first opening formed on the outer surface of the balancer shaft at a first location associated with the cylinder A in the cylinder row direction; a second opening formed on the outer surface at a second location associated with the cylinder C in the cylinder row direction; and a communication passage formed inside the balancer shaft so as to connect the first opening with the second opening.

An engine balance shaft (20) for an internal combustion engine (24) is provided having reduced total mass and rotational inertia while having sufficient bending stiffness and sufficient unbalance mass. The balance shaft (20) is formed by fixedly coupling a counterweight (56), a front bearing journal (68), a rear bearing journal (60), a tail piece (40), and a nose piece (44) to a hollow tube (52). The hollow tube (52) is hydroformed to expand the diameter of the tube and fasten the desired components to the tube (52).

A crank chamber internal pressure reduction mechanism for internal combustion engine includes a crankshaft, a rotating shaft (a balancer shaft), a suction mechanism (a primary drive gear), a first discharge passage (a discharge passage, a joining passage, and a discharge hose), and a second discharge passage (a discharge passage). The crankshaft is rotatably supported to a crankcase. To the rotating shaft, a rotation force is transmitted from the crankshaft. The suction mechanism is disposed at the rotating shaft. The suction mechanism rotates integrally with the rotating shaft. To the first discharge passage, the emission is discharged from the crank chamber. The second discharge passage is communicated with the first discharge passage. The second discharge passage is disposed inside the rotating shaft. The suction mechanism includes a third discharge passage (a hole). The third discharge passage is communicated with the second discharge passage. The third discharge passage extends outside the rotating shaft in a radial direction to communicate with an external space.

A crank chamber internal pressure reduction mechanism for internal combustion engine includes a crankshaft, a rotating shaft (a balancer shaft), a suction mechanism (a primary drive gear), a first discharge passage (a discharge passage, a joining passage, and a discharge hose), and a second discharge passage (a discharge passage). The crankshaft is rotatably supported to a crankcase. To the rotating shaft, a rotation force is transmitted from the crankshaft. The suction mechanism is disposed at the rotating shaft. The suction mechanism rotates integrally with the rotating shaft. To the first discharge passage, the emission is discharged from the crank chamber. The second discharge passage is communicated with the first discharge passage. The second discharge passage is disposed inside the rotating shaft. The suction mechanism includes a third discharge passage (a hole). The third discharge passage is communicated with the second discharge passage. The third discharge passage extends outside the rotating shaft in a radial direction to communicate with an external space.