reference will now be made in detail to various embodiments of the present invention ( s ), examples of which are illustrated in the accompanying drawings and described below . while the invention ( s ) will be described in conjunction with exemplary embodiments , it will be understood that the present description is not intended to limit the invention ( s ) to those exemplary embodiments . on the contrary , the invention ( s ) is / are intended to cover not only the exemplary embodiments , but also various alternatives , modifications , equivalents and other embodiments , which may be included within the spirit and scope of the invention as defined by the appended claims . hereinafter , an exemplary embodiment of the present invention will be described with reference to the accompanying drawings so that those skilled in the field of the invention to which the present invention pertains may carry out the exemplary embodiment . fig1 is a cross - sectional view illustrating a cylinder head having an oil supply passage according to an exemplary embodiment of the present invention . as illustrated in fig1 , an oil supply passage according to an exemplary embodiment of the present invention may be formed in both a cylinder head 10 and a cam carrier 12 . as the cylinder head 10 , the cam carrier 12 and the cam cap 14 are engaged with one another , the oil supply passage formed in both the cylinder head 10 and the cam carrier 12 may be a sealed passage . the cylinder head 10 , the cam carrier 12 and the cam cap 14 may be engaged with one another by an engaging device 15 such as a bolt or any other similar engaging device fig2 is a perspective view illustrating an oil supply passage according to an exemplary embodiment of the present invention . fig3 is a front view illustrating an oil supply passage according to an exemplary embodiment of the present invention . fig4 is a top plan view illustrating an oil supply passage according to an exemplary embodiment of the present invention . as illustrated in fig2 to 4 , the oil passage for supplying oil may include a high pressure passage 100 and a low pressure passage 200 . the high pressure passage 100 may be an oil passage that maintains a high pressure since it receives a high pressure oil with the aid of an oil supply apparatus 20 such as an oil pump , etc . in an air - tightness state . the low pressure passage 200 may be an oil passage that maintains constant an internal hydraulic pressure since it receives oil from the high pressure passage 100 in the air - tightness state . the hydraulic pressure in the low pressure passage 200 is relatively lower than that in the high pressure passage 100 . the high pressure passage 100 may include a main gallery 102 , 104 , a cross gallery 106 , 108 , a supply gallery 105 and a connection gallery 107 . the main gallery 102 , 104 may be longitudinally arranged in a direction where a plurality of cylinders is positioned . the main gallery 102 , 104 may include a lower main gallery 102 and an upper main gallery 104 . in an aspect of the present invention , the lower main gallery 102 may be positioned in the cylinder head 10 . the lower main gallery 102 may include two or more lower main galleries 102 , the two or more lower main galleries 102 being positioned in parallel with each other . as illustrated in fig2 and fig4 , two lower main galleries 102 are positioned in parallel with each other at both a first side and a second side of the cylinder head 10 . the upper main gallery 104 may be positioned in the cam carrier 12 . the upper main gallery 104 may include two or more upper main galleries 104 , the two or more upper main galleries 104 being positioned in parallel with each other . as illustrated in fig2 and fig4 , two upper man galleries 104 are positioned in parallel with each other . the cross gallery 106 , 108 may be connected across the at least two main galleries 102 and 104 that may be longitudinally formed in a direction where a plurality of cylinders are positioned . the cross gallery 106 , 108 may include a lower cross gallery 106 and an upper cross gallery 108 . the lower cross gallery 106 may be connected across at last two lower main galleries 102 that are arranged in parallel with each other . as illustrated in fig2 and fig4 , a lower cross gallery 106 connects the two lower main galleries 102 but not limited thereto . the upper cross gallery 108 may be connected across two or more upper main galleries 104 that are arranged in parallel with each other . as illustrated in fig2 and fig4 , three upper cross galleries 108 connect the two lower main galleries 102 . referring to fig3 and 4 , the supply gallery 105 may be a passage through which to supply oil from the oil supply apparatus 20 to the high pressure passage 100 . further , the supply gallery 105 may be connected to either a lower main gallery 102 or a lower cross gallery 106 so as to supply oil to the high pressure passage 100 . as illustrated in fig3 , the supply gallery 105 is connected to the lower main gallery 102 . the connection gallery 107 may be a passage that connects either the lower main gallery 102 or the lower cross gallery 106 or connects the upper main gallery 104 or the upper cross gallery 108 . further , the hydraulic pressures of the lower high pressure passage which includes the lower main gallery 102 and the lower cross gallery 106 and the hydraulic pressures of the upper high pressure passages including the upper main gallery 104 and the upper cross gallery 108 are maintained same by the connection gallery 107 . as illustrated in fig2 to fig4 , the connection gallery 107 connects the lower cross gallery 106 and the upper cross gallery 108 . the upper high pressure passage may further include a camshaft gallery 120 where the hydraulic pressure is also maintained by the connection gallery 107 the camshaft gallery 120 may be formed in an arch shape in whole to surround the lower surface of the camshaft . further , both a first end and a second end of the arch - shaped camshaft gallery 120 may be formed in circular shapes . both the first and the second ends of the camshaft gallery 120 may be formed in circular shapes because a passage can be formed where the engaging device 15 such as a bolt , etc . may be surrounded . that is , the engaging device 15 may be inserted and engaged into a hollow portion of the circular shape of the camshaft gallery 120 . the hollow portion of the circular shape of the camshaft gallery 120 may be called a bolt through hole 122 . a first end portion of both the first end and the second end of the camshaft gallery 120 where the circular shape is formed may be connected to the upper main gallery 104 . a second end portion of both the first and second ends of the camshaft gallery 120 where the circular shape is formed may be connected to the low pressure passage 200 . the low pressure passage 200 may include a low pressure main gallery 202 , a low pressure cross gallery 206 and a low pressure supply gallery 208 . the low pressure main gallery 202 may be longitudinally formed in a direction where a plurality of the cylinders is arranged . the low pressure main gallery 202 may be formed in the cylinder head 10 . in addition , the low pressure main gallery 202 may include at least two low pressure main galleries 202 that are parallel with each other . as illustrated in fig2 and fig4 , two low pressure main galleries 202 are arranged in parallel at both the first and the second sides of the cylinder head 10 . the low pressure cross gallery 206 may be connected across at least two low pressure main galleries 202 that may be longitudinally formed in a direction where a plurality of the cylinders are arranged . as illustrated in fig2 and fig4 , two low pressure cross galleries 206 connect two low pressure main galleries 202 , but not limited thereto . in an aspect of the present invention , the low pressure supply gallery 208 may be positioned in the low pressure cross gallery 206 . further , the low pressure supply gallery 208 may be a passage through which to supply oil to the cylinder deactivation apparatus ( cda ) 30 . the cylinder deactivation apparatus ( cda ) 30 may be an apparatus that deactivates part of a plurality of the cylinders installed in an engine when the engine is in a low horse power state , which construction is well known to a person having ordinary skill in the art , so the descriptions thereon will be omitted . in particular , the oil passage for supplying oil is connected to supply hydraulic pressure to the cylinder deactivation apparatus ( cda ) 30 when the cylinder deactivation apparatus ( cda ) 30 operates by hydraulic pressure . meanwhile , the hydraulic pressure of the low pressure passage 200 that is relatively lower than that in the high pressure passage 100 maintains a hydraulic pressure high enough to drive the cylinder deactivation apparatus ( cda ) 30 . the low pressure cross gallery 206 is provided with more than the number of the cylinders that are deactivated by the operation of the cylinder deactivation apparatus ( cda ) 30 , and the low pressure supply gallery 208 is provided with the number of the cylinders that will be deactivated . the oil passage for supplying oil may further include an orifice 130 , a valve hole 110 , a valve drain hole 112 , and a drainage passage 140 . the orifice 130 may be a passage that connects the high pressure passage 100 and the low pressure passage 200 . that is , the orifice 130 may be formed in the second end portion of both the first and second ends of the camshaft galley 120 connected to the low pressure passage 200 and may be connected to the low pressure cross galley 206 of the low pressure passage 200 . the low pressure cross gallery 206 may extend upwards to be coupled to the second end portion of both the first and second ends of the cam shaft gallery 120 through the orifice 130 and then extends across the low pressure main gallery 202 . further , the orifice 130 may be formed to maintain constant the hydraulic pressure of the low pressure passage 200 . the orifice 130 may channel oil from the high pressure passage 100 to the low pressure passage 200 when the hydraulic pressure of the low pressure passage 200 is lower than the predetermined hydraulic pressure , so the hydraulic pressure of the low pressure passage 200 rises to the predetermined hydraulic pressure and is maintained constant . the orifice 130 may be a passage for oil so as to channel the flow of oil in such a way that part of the passage is made narrower , so the orifice passes oil with less resistance in liquidity as compared with its length . the definition and function of the orifice are known to a person having an ordinary skill in the art , so the descriptions thereon will be omitted . in an aspect of the present invention , the orifice 130 that allows the low pressure passage 200 to constantly maintain low pressure may be integrally formed in the cylinder head 10 , so it is possible to remove the constituent elements that were necessary when installing the orifice . the valve hole 110 is a hole in which is positioned an oil control valve 40 that controls the amount of oil that is supplied to the cylinder deactivation apparatus ( cda ) 30 . that is , the low pressure supply galley 208 communicates with the valve hole 110 so as to supply hydraulic pressure to the oil control valve 40 . the oil control valve 40 that is opened and closed so as to adjust the amount of oil that is supplied to the portions which need oil is known to a person having ordinary skill in the art , so the descriptions thereon will be omitted . the valve drain hole 112 may be positioned at an end of the valve hole 110 and communicates with the valve hole 110 . in addition , the valve drain hole 112 is formed to supply oil to the cylinder deactivation apparatus ( cda ) 30 and to drain the oil remaining in the oil control valve 40 . the drainage passage 140 may be formed to drain the oil of the high pressure passage 100 when the hydraulic pressure of the high pressure passage 100 becomes excessively high . the oil drained through the drainage passage 140 may be supplied to the portions of a vehicle which need oil . for example , the oil drained through the drainage passage 140 may be used for the elements that are operatively provided in the engine and that need lubrication . referring to fig3 and fig4 , the flow of the oil flowing through the oil passage for supplying oil is indicated by arrows . in an aspect of the present invention , the oil that is supplied to the high pressure passage 100 through the supply gallery 105 flows through the galleries of the high pressure passage 100 connected so that the high pressure is uniformly formed in the high pressure passage 100 . when the drainage passage 140 is selectively opened , part of the oil that moves through the galleries of the high pressure passage 100 can be drained . the oil that is supplied through the orifice 130 from the high pressure passage 100 to the low pressure passage 200 flows through the galleries of the thusly connected low pressure passage 200 so that the low pressure can be uniformly formed in the entire portions of the low pressure passage 200 . when the oil control valve 40 is selectively opened , part of the oil that flows through the galleries of the low pressure passage 200 is supplied to the cylinder deactivation apparatus ( cda ) 30 . thus , a low pressure is uniformly formed in the entire portions of the low pressure passage 200 based on the function of the orifice 130 and is maintained . in an aspect of the present invention , the construction of the oil passage for supplying oil can be simplified since the orifice 130 is integrally formed in the cylinder head 10 without adding elements that were necessary in the orifice . further , the construction of the oil supply passages 100 and 200 is simple , so the manufacture cost may decrease , and the manufacture process may become simpler . since a hydraulic pressure is constantly maintained in the low pressure passage 200 , efficient and accurate oil supply can be obtained . therefore , the reactivity can be improved . for convenience in explanation and accurate definition in the appended claims , the terms “ upper ”, “ lower ”, “ inner ” and “ outer ” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures . the foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description . they are not intended to be exhaustive or to limit the invention to the precise forms disclosed , and obviously many modifications and variations are possible in light of the above teachings . the exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application , to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention , as well as various alternatives and modifications thereof . it is intended that the scope of the invention be defined by the claims appended hereto and their equivalents .