Internal combustion engine and method for manufacturing internal combustion engine

An oil separator connected to a blow-by gas passage and an intake passage of an internal combustion engine, wherein the blow-by gas passage is defined inside a cylinder block to return blow-by gas to the intake passage, and in a state in which the internal combustion engine is mounted on a vehicle, an up-down direction of the vehicle is referred to as a vertical direction, and a plane orthogonal to the vertical direction is referred to as a horizontal plane, the blow-by gas passage includes a first blow-by gas passage portion open downward in the vertical direction of the cylinder block, wherein the first blow-by gas passage portion extends upward in the vertical direction of the cylinder block from an opening directed downward in the vertical direction, and a second blow-by gas passage portion continuous with the first blow-by gas passage portion, wherein the second blow-by gas passage portion extends so that an inclination angle of an extension direction of the second blow-by gas passage portion relative to the horizontal plane is less than an inclination angle of an extension direction of the first blow-by gas passage portion relative to the horizontal plane, and the second blow-by gas passage portion opens in an outer surface of the cylinder block, the oil separator comprising:

• a separation portion located upward from an opening of the second blow-by gas passage portion in the outer surface of the cylinder block, wherein the separation portion is configured to separate oil from the blow-by gas, and
• a connection passage that connects the separation portion and the second blow-by gas passage portion, wherein
• at least part of the connection passage located toward the second blow-by gas passage portion serves as a first passage portion, wherein the first passage portion is configured to extend so that an inclination angle of the first passage portion relative to the horizontal plane is less than an inclination angle of an extension direction of the first blow-by gas passage portion relative to the horizontal plane, and
• the second blow-by gas passage portion and the first passage portion of the connection passage are referred to as an intermediate passage, and a step is arranged in the intermediate passage at an intermediate portion with respect to an extension direction, wherein the intermediate passage has a cross-sectional area at a downstream side with respect to a flow direction of the blow-by gas that is smaller than a cross-sectional area of the intermediate passage at an upstream side with respect to the flow direction of the blow-by gas.

A method for manufacturing an internal combustion engine, the method comprising:

• forming a blow-by gas passage inside a cylinder block to return blow-by gas to an intake passage;
• providing an oil separator to separate oil from the blow-by gas;
• and
• connecting the oil separator to the blow-by gas passage and the intake passage, wherein
• in a state in which the internal combustion engine is mounted on a vehicle, an up-down direction of the vehicle is referred to as a vertical direction, and a plane orthogonal to the vertical direction is referred to as a horizontal plane,
• the forming a blow-by gas passage includes
• forming a first blow-by gas passage portion open downward in the vertical direction of the cylinder block, wherein the first blow-by gas passage portion extends upward in the vertical direction of the cylinder block from an opening of the first blow-by gas passage portion directed downward in the vertical direction, and
• forming a second blow-by gas passage portion continuously with the first blow-by gas passage portion, wherein the second blow-by gas passage portion extends so that an inclination angle of an extension direction of the second blow-by gas passage portion relative to the horizontal plane is less than an inclination angle of an extension direction of the first blow-by gas passage portion relative to the horizontal plane, and the second blow-by gas passage portion opens in an outer surface of the cylinder block,
• the providing an oil separator includes
• forming a separation portion located upward from an opening of the second blow-by gas passage portion in the outer surface of the cylinder block, wherein the separation portion is configured to separate oil contained in blow-by gas,
• forming a connection passage connecting the separation portion and the second blow-by gas passage portion, and
• forming a first passage portion that is at least part of the connection passage located toward the second blow-by gas passage portion, wherein the first passage portion extends so that an inclination angle of the first passage portion relative to the horizontal plane is less than an inclination angle of an extension direction of the first blow-by gas passage portion relative to the horizontal plane, and
• the connecting the oil separator to the blow-by gas passage and the intake passage includes
• when the second blow-by gas passage portion and the first passage portion of the connection passage are referred to as an intermediate passage, arranging a step in the intermediate passage at an intermediate portion with respect to an extension direction of the intermediate passage, wherein the intermediate passage has a cross-sectional area at a downstream side with respect to a flow direction of the blow-by gas that is smaller than a cross-sectional area of the intermediate passage at an upstream side with respect to the flow direction of the blow-by gas.