Patent ID: 8904773

Claim:
A cooling water passage structure in a cylinder head of an internal combustion engine, comprising: a first exhaust-side cooling water passage and a second exhaust-side cooling water passage arranged to sandwich an exhaust collecting portion of the cylinder head and extending in a lengthwise direction of the cylinder head, the exhaust collecting portion being formed in the cylinder head to define an exhaust opening in an exhaust-side lateral surface of the cylinder head and to collect exhaust gases exhausted from a plurality of combustion chambers which are arrayed in a line, an exhaust pipe being fastened to the exhaust-side lateral surface of the cylinder head via a fastening member and being adapted to arrange an exhaust cleaner immediately downstream of the exhaust opening; and a shunt passage formed in at least one of the first exhaust-side cooling water passage and the second exhaust-side cooling water passage to cool the fastening member, the shunt passage being formed along a water flow in the first exhaust-side cooling water passage or the second exhaust-side cooling water passage by partly expanding a part of a lateral edge of the first exhaust-side cooling water passage or the second exhaust-side cooling water passage on a side close to the exhaust-side lateral surface to increase a passage cross-sectional area of the first exhaust-side cooling water passage or the second exhaust-side cooling water passage, wherein the shunt passage including a first shunt passage and a second shut passage, the first shunt passage being formed to bypass a fastening boss portion in a direction in which the fastening member is fastened to the fastening boss portion, the second shunt passage being formed sandwiched between the fastening boss portion facing the exhaust collecting portion and the exhaust collecting portion to cool the surface of the fastening boss portion on a side close to the exhaust collecting portion.