Internal combustion engine

1. An internal combustion engine comprising:

a main combustion chamber sandwiched between a cylinder head and a piston facing the cylinder head;

an intake port formed within the cylinder head and connected to the main combustion chamber at an intake opening;

an exhaust port formed within the cylinder head and connected to the main combustion chamber at an exhaust opening;

a sub-chamber provided on the cylinder head between the intake opening and the exhaust opening, and connected to the main combustion chamber through a plurality of through-holes;

a fuel injector injecting fuel into the sub-chamber; and

a spark plug performing ignition in the sub-chamber, wherein

a tumble flow at a position of the sub-chamber flows from a first side to a second side as seen from the sub-chamber,

the plurality of through-holes include:

a first through-hole formed in a part on the first side of a side wall of the sub-chamber; and

a second through-hole different from the first through-hole and formed in a part on the second side of the side wall of the sub-chamber,

a diameter of the first through-hole is larger than a diameter of the second through-hole, and

the fuel injector preferentially injects fuel to a direction of the second side over a direction of the first side.

2. The internal combustion engine according to claim 1 , wherein

the first through-hole and the second through-hole face each other.

3. The internal combustion engine according to claim 1 , wherein

there is no fuel injector in the intake port nor in the main combustion chamber.

4. The internal combustion engine according to claim 1 , wherein

the fuel injector injects fuel of a first injection amount into the sub-chamber in an intake stroke, and

the fuel injector injects fuel of a second injection amount less than the first injection amount into the sub-chamber after the intake stroke and before an ignition timing.

5. The internal combustion engine according to claim 1 , wherein

the plurality of through-holes further include a third through-hole, and

the third through-hole is provided such that the fuel injected from the fuel injector passes through the third through-hole to directly enter the main combustion chamber.

6. An internal combustion engine comprising:

a main combustion chamber sandwiched between a cylinder head and a piston facing the cylinder head;

an intake port formed within the cylinder head and connected to the main combustion chamber at an intake opening;

an exhaust port formed within the cylinder head and connected to the main combustion chamber at an exhaust opening;

a sub-chamber provided on the cylinder head between the intake opening and the exhaust opening, and connected to the main combustion chamber through a plurality of through-holes;

a fuel injector injecting fuel into the sub-chamber; and

a spark plug performing ignition in the sub-chamber, wherein

the plurality of through-holes include:

a first through-hole formed in a part on a side of the intake opening of a side wall of the sub-chamber; and

a second through-hole different from the first through-hole and formed in a part on a side of the exhaust opening of the side wall of the sub-chamber,

a diameter of the first through-hole is larger than a diameter of the second through-hole, and

the fuel injector preferentially injects fuel to a direction of the side of the exhaust opening over a direction of the side of the intake opening.