Cylinder head structure of engine

Abstract

The first flow-restriction vertical bead narrowing the coolant flow is provided to increase the flow speed at this portion. The coolant passage opens at the flow-in area between the exhaust ports. Thereby, the flow speed of the coolant at this area is increased, so the coolant in the coolant passage can be properly sucked due to the Venturi effect. As a result, the cooling function can be improved.

1 . A cylinder head structure of an engine, in which the engine has a multiple cylinders, there is provided for each cylinder a valve unit comprising two intake valves and two exhaust valves and an ignition plug located at a substantially central portion of the cylinder, and there are provided a main water jacket to allow part of a coolant to flow around each ignition-plug hole wall in a cylinder-row direction and an exhaust-side sub water jacket to allow part of the coolant to flow around each exhaust port wall in the cylinder-row direction, the both water jackets being connected to each other, the cylinder structure comprising: 
 a first vertical bead portion that is formed at a portion of the ignition-plug hole wall that is opposed to the exhaust port wall, the first vertical bead portion providing a smallest cross section of a passage between the ignition-plug hole wall and the exhaust port wall in said main water jacket;    a second vertical bead portion that is formed at a portion of the ignition-plug hole wall that is opposed to an intake port wall, the second vertical bead portion providing a smallest cross section of a passage between the ignition-plug hole wall and the intake port wall in said main water jacket; and    a coolant passage that is provided between a pair of exhaust port walls of the cylinder, one end of the coolant passage opening at a cylinder-head lower face and the other thereof opening at a location that is opposed to the ignition plug hole wall,    wherein said smallest cross section provided by the first vertical bead portion is configured so as to be greater than said smallest cross section provided by the second vertical bead portion, and said first vertical bead portion formed at the ignition-plug hole wall is configured so as to be opposed to the exhaust port wall that is located at an upstream side of the flow direction of the coolant.    
   
   
       2 . The cylinder head structure of an engine of  claim 1 , wherein an exhaust-side passage portion restricted by said first vertical bead portion is configured so as to be higher in a vertical direction than an intake-side passage portion restricted by said second vertical bead portion, and said first vertical bead portion is configured so as to be longer in the vertical direction than said second vertical bead portion.  
   
   
       3 . The cylinder head structure of an engine of  claim 2 , wherein said exhaust-side passage portion restricted by the first vertical bead portion has a substantially constant width over a height thereof.  
   
   
       4 . The cylinder head structure of an engine of  claim 1 , wherein said second vertical bead portion formed at the ignition-plug hole wall is configured so as to be opposed to the intake port wall that is located at a downstream side of the flow direction of the coolant.  
   
   
       5 . The cylinder head structure of an engine of  claim 1 , wherein there is provided an intake-side sub water jacket that is located below the intake ports of each cylinder to connect with said main water jacket, a fuel-injector hole wall to accommodate a fuel injector is formed at a portion that is between a pair of intake ports and below the intake ports, and said fuel-injector hole wall is located in said intake-side sub water jacket.