Cooling structure for internal combustion engine

A cooling structure of an internal combustion engine, in which:

• said internal combustion engine is mounted at a center in a left-right vehicle-width direction of a vehicle body between a front wheel and a rear wheel of a motorcycle,
• said internal combustion engine has an engine body configured to place a cylinder block and a cylinder head in this order on a crankcase,
• said cylinder block has an in-cylinder-block fluid passage through which a coolant flows around a cylinder bore,
• said cylinder head has an in-cylinder-head fluid passage through which said coolant flows around a combustion chamber, and
• a via-radiator passage passing through a radiator air-cooling said coolant and a bypass passage bypassing said radiator are installed to a coolant circulation path circulating said coolant through said in-cylinder-block fluid passage and said in-cylinder-head fluid passage by a coolant pump,
• said cooling structure of said internal combustion engine, comprising a thermostat provided to switch between a circulation by way of said via-radiator passage and a circulation by way of said bypass passage,
• wherein:
• said in-cylinder-block fluid passage is partitioned up and down in an axis direction of a cylinder axis into an in-cylinder-block upper fluid passage and an in-cylinder-block lower fluid passage by a partition wall, said cylinder axis being a central axis of said cylinder bore,
• said bypass passage is partially composed of said in-cylinder-block lower fluid passage,
• said in-cylinder-block upper fluid passage and said in-cylinder-head fluid passage communicate with each other via a communication hole of a gasket which is sandwiched between said cylinder block and said cylinder head,
• said thermostat has a thermostat case that is integrally formed in said cylinder head in an outflow section of said in-cylinder-head fluid passage,
• said thermostat is operative to cause said coolant flowing out from said in-cylinder-head fluid passage to flow to either said via-radiator passage or said bypass passage in a selective manner, and
• said in-cylinder-head fluid passage includes an escape passage through which a portion of said coolant flowing out from said in-cylinder-head fluid passage escapes into said bypass passage at all times.

A cooling structure of an internal combustion engine, in which

• said internal combustion engine is mounted at a center in a left-right vehicle-width direction of a vehicle body between a front wheel and a rear wheel of a motorcycle,
• said internal combustion engine has an engine body configured to place a cylinder block and a cylinder head in this order on a crankcase,
• said cylinder block has an in-cylinder-block fluid passage through which a coolant flows around a cylinder bore,
• said cylinder head has an in-cylinder-head fluid passage through which said coolant flows around a combustion chamber, and
• a via-radiator passage passing through a radiator air-cooling said coolant and a bypass passage bypassing said radiator are installed to a coolant circulation path circulating said coolant through said in-cylinder-block fluid passage and said in-cylinder-head fluid passage by a coolant pump,
• said cooling structure of said internal combustion engine, comprising a thermostat provided to switch between a circulation by way of said via-radiator passage and a circulation by way of said bypass passage,
• wherein:
• said in-cylinder-block fluid passage is partitioned up and down in an axis direction of a cylinder axis into an in-cylinder-block upper fluid passage and an in-cylinder-block lower fluid passage by a partition wall, said cylinder axis being a central axis of said cylinder bore,
• said bypass passage is partially composed of said in-cylinder-block lower fluid passage,
• said in-cylinder-head fluid passage includes an escape passage through which a portion of said coolant flowing out from said in-cylinder-head fluid passage escapes into said bypass passage at all times,
• said in-cylinder-block lower fluid passage has a lower fluid passage outlet formed therein, said in-cylinder-block upper fluid passage has an upper fluid passage inlet formed therein, and said lower fluid passage outlet and said upper fluid passage inlet are formed adjacent to each other in said front wall of said cylinder block, and
• said lower fluid passage outlet is connected to a lower fluid passage outflow connection tube, said upper fluid passage inlet is connected to an upper fluid passage inflow connection tube, and said lower fluid passage outflow connection tube and said upper fluid passage inflow connection tube are integrally formed.