Patent ID: 8220425

Claim:
A valve operation control system for an internal combustion engine comprising a hydraulic valve operation mode changing mechanism ( 63 , 75 ) for switching the operation mode of an engine valve (VI, VE) openably and closably disposed in a cylinder head ( 22 R), and hydraulic pressure control means ( 108 R) for controlling hydraulic pressure that is applied to the valve operation mode changing mechanism ( 63 , 75 ), the hydraulic pressure control means ( 108 R) comprising a holder ( 109 ) mounted on the cylinder head ( 22 R), a spool valve ( 111 , 112 ) formed by slidably housing a spool valve body ( 123 , 125 ) in a valve body ( 110 ) provided so as to be connected to the holder ( 109 ), the spool valve body ( 123 , 125 ) having one end part facing a pilot hydraulic chamber ( 122 , 124 ), and an electromagnetic open/close valve ( 113 , 114 ) for controlling hydraulic pressure of the pilot hydraulic chamber ( 122 , 124 ), characterized in that the holder ( 109 ) is formed by integrally connecting a housed portion ( 109 a ) and a projecting portion ( 109 b ) by means of a connection portion ( 109 c ), the housed portion ( 109 a ) being housed between the cylinder head ( 22 R) and a head cover ( 23 R) secured to the cylinder head ( 22 R), the projecting portion ( 109 b ) projecting outside the cylinder head ( 22 R) and the head cover ( 23 R) and having the electromagnetic open/close valve ( 113 , 114 ) mounted thereon, a seal face ( 116 , 117 ) between the head cover ( 23 R) and the cylinder head ( 22 R) is formed on the connection portion ( 109 c ), and the valve body ( 110 ) is provided so as to be connected to the housed portion ( 109 a ) while being housed between the head cover ( 23 R) and the cylinder head ( 22 R).