Patent Publication Number: US-9840961-B2

Title: Cylinder head of an internal combustion engine

Description:
TECHNICAL FIELD 
     Various embodiments relate to a cylinder head of an internal combustion engine and cooling thereof. 
     BACKGROUND 
     Internal combustion engines may require cooling during engine operation based on heat produced by the in-cylinder combustion process. The engine may be formed from a cylinder block and a cylinder head that cooperate to define a cylinder. The engine block and cylinder head may have various passages formed therein to provide coolant flow through the engine to control the temperature during operation. 
     SUMMARY 
     In an embodiment, a cylinder head is provided with a member defining a cooling jacket having a first longitudinal passage with an annular section about a spark plug, a second longitudinal passage with an annular section about an exhaust valve, and a third passage surrounding an integrated exhaust manifold and fluidly connecting the first and second passages. The first passage has a continuously decreasing area and the second passage has a continuously increasing area in a direction of coolant flow. 
     In another embodiment, an engine is provided with a cylinder head having a deck face to mate with a corresponding face of a cylinder block. The head defines a coolant jacket therein that is formed from a series of passages interconnected by a series of curved junctions to direct coolant about spark plugs, exhaust valves, and an integrated exhaust manifold in the head. Each passage in the cooling jacket has a length that is greater than an average effective diameter of the passage. 
     In yet another embodiment, an engine component has a cylinder head defining a cooling jacket. The cooling jacket has a first passage extending longitudinally from a first end region to a second end region of the head, with the first passage having a continuously decreasing cross-sectional area towards the second end region and in a direction of coolant flow therethrough. The first passage having a series of annular regions, each annular region surrounding a recess sized to receive a spark plug. The cooling jacket has a second passage extending longitudinally from the second end region to the first end region of the head, with the second passage having a continuously increasing cross-sectional area towards the first end region and in a direction of coolant flow therethrough. The second passage receives coolant from the first passage. The second passage has a series of pairs of annular regions, with each pair of annular regions surrounding a pair of recesses sized to receive a pair of exhaust valves. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic of an internal combustion engine capable of implementing the disclosed embodiments; 
         FIG. 2  illustrates a perspective view of cores for a conventional cooling jacket system and a core for a cooling jacket according to an embodiment; 
         FIG. 3  illustrates a perspective view of a cooling jacket according to an embodiment; 
         FIG. 4  illustrates another perspective view of the cooling jacket of  FIG. 3 ; 
         FIG. 5  illustrates a flow schematic of the cooling jacket of  FIG. 3 ; 
         FIG. 6  illustrates a flow schematic of a cooling jacket according to another embodiment; and 
         FIG. 7  illustrates a flow schematic of a cooling jacket according to yet another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present disclosure are provided herein; however, it is to be understood that the disclosed embodiments are merely exemplary and may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure. 
       FIG. 1  illustrates a schematic of an internal combustion engine  20 . The engine  20  has a plurality of cylinders  22 , and one cylinder is illustrated. The engine  20  may have any number of cylinders, and the cylinders may be arranged in various configurations. The engine  20  has a combustion chamber  24  associated with each cylinder  22 . The cylinder  22  is formed by cylinder walls  32  and piston  34 . The piston  34  is connected to a crankshaft  36 . The combustion chamber  24  is in fluid communication with the intake manifold  38  and the exhaust manifold  40 . An intake valve  42  controls flow from the intake manifold  38  into the combustion chamber  24 . An exhaust valve  44  controls flow from the combustion chamber  24  to the exhaust system(s)  40  or exhaust manifold. The intake and exhaust valves  42 ,  44  may be operated in various ways as is known in the art to control the engine operation. 
     A fuel injector  46  delivers fuel from a fuel system directly into the combustion chamber  24  such that the engine is a direct injection engine. A low pressure or high pressure fuel injection system may be used with the engine  20 , or a port injection system may be used in other examples. An ignition system includes a spark plug  48  that is controlled to provide energy in the form of a spark to ignite a fuel air mixture in the combustion chamber  24 . The spark plug  48  may be positioned overhead or to one side of the cylinder  22 . In other embodiments, other fuel delivery systems and ignition systems or techniques may be used, including compression ignition. 
     The engine  20  includes a controller and various sensors configured to provide signals to the controller for use in controlling the air and fuel delivery to the engine, the ignition timing, the power and torque output from the engine, the exhaust system, and the like. Engine sensors may include, but are not limited to, an oxygen sensor in the exhaust system  40 , an engine coolant temperature sensor, an accelerator pedal position sensor, an engine manifold pressure (MAP) sensor, an engine position sensor for crankshaft position, an air mass sensor in the intake manifold  38 , a throttle position sensor, an exhaust gas temperature sensor in the exhaust system  40 , and the like. 
     In some embodiments, the engine  20  is used as the sole prime mover in a vehicle, such as a conventional vehicle, or a stop-start vehicle. In other embodiments, the engine may be used in a hybrid vehicle where an additional prime mover, such as an electric machine, is available to provide additional power to propel the vehicle. 
     Each cylinder  22  may operate under a four-stroke cycle including an intake stroke, a compression stroke, an ignition stroke, and an exhaust stroke. In other embodiments, the engine may operate with a two stroke cycle. During the intake stroke, the intake valve  42  opens and the exhaust valve  44  closes while the piston  34  moves from the top of the cylinder  22  to the bottom of the cylinder  22  to introduce air from the intake manifold to the combustion chamber. The piston  34  position at the top of the cylinder  22  is generally known as top dead center (TDC). The piston  34  position at the bottom of the cylinder is generally known as bottom dead center (BDC). 
     During the compression stroke, the intake and exhaust valves  42 ,  44  are closed. The piston  34  moves from the bottom towards the top of the cylinder  22  to compress the air within the combustion chamber  24 . 
     Fuel is introduced into the combustion chamber  24  and ignited. In the engine  20  shown, the fuel is injected into the chamber  24  and is then ignited using spark plug  48 . In other examples, the fuel may be ignited using compression ignition. 
     During the expansion stroke, the ignited fuel air mixture in the combustion chamber  24  expands, thereby causing the piston  34  to move from the top of the cylinder  22  to the bottom of the cylinder  22 . The movement of the piston  34  causes a corresponding movement in crankshaft  36  and provides for a mechanical torque output from the engine  20 . 
     During the exhaust stroke, the intake valve  42  remains closed, and the exhaust valve  44  opens. The piston  34  moves from the bottom of the cylinder to the top of the cylinder  22  to remove the exhaust gases and combustion products from the combustion chamber  24  by reducing the volume of the chamber  24 . The exhaust gases flow from the combustion cylinder  22  to the exhaust system  40  as described below and to an after-treatment system such as a catalytic converter. 
     The intake and exhaust valve  42 ,  44  positions and timing, as well as the fuel injection timing and ignition timing may be varied for the various engine strokes. 
     The engine  20  has a cylinder block  70  and a cylinder head  72  that cooperate with one another to form the combustion chambers  24 . A head gasket (not shown) may be positioned between the block  70  and the head  72  to seal the chamber  24 . The cylinder block  70  has a block deck face that corresponds with and mates with a head deck face of the cylinder head  72  along part line  74 . 
     The engine  20  includes a fluid system  80 . In one example, the fluid system  80  is a cooling system  80  to remove heat from the engine  20 . In another example, the fluid system  80  is a lubrication system  80  to lubricate engine components. 
     For a cooling system  80 , the amount of heat removed from the engine  20  may be controlled by a cooling system controller, the engine controller, one or more thermostats, and the like. The system  80  may be integrated into the engine  20  as one or more cooling jackets that are cast, machined, or other formed in the engine. The system  80  has one or more cooling circuits that may contain an ethylene glycol/water antifreeze mixture, another water-based fluid, or another coolant as the working fluid. In one example, the cooling circuit has a first cooling jacket  84  in the cylinder block  70  and a second cooling jacket  86  in the cylinder head  72  with the jackets  84 ,  86  in fluid communication with each other. In another example, jacket  86  is independently controlled and is separate from jacket  84 . Coolant in the cooling circuit  80  and jackets  84 ,  86  flows from an area of high pressure towards an area of lower pressure. 
     The fluid system  80  has one or more pumps  88 . In a cooling system  80 , the pump  88  provides fluid in the circuit to fluid passages in the cylinder block  70 , and then to the head  72 . The cooling system  80  may also include valves or thermostats (not shown) to control the flow or pressure of coolant, or direct coolant within the system  80 . The cooling passages in the cylinder block  70  may be adjacent to one or more of the combustion chambers  24  and cylinders  22 . Similarly, the cooling passages in the cylinder head  72  may be adjacent to one or more of the combustion chambers  24  and the exhaust ports for the exhaust valves  44 . Fluid flows from the cylinder head  72  and out of the engine  20  to a heat exchanger  90  such as a radiator where heat is transferred from the coolant to the environment. 
       FIG. 2  illustrates a perspective view of cores used to form a conventional upper cooling jacket  100  and lower cooling jacket  102  for a cylinder head. The conventional jackets  100 ,  102  may be generally designed to occupy a large portion of the cylinder head to distribute coolant therethrough in an open jacket configuration. A cooling jacket  200  according to the present disclosure is also illustrated in  FIG. 2  for comparison, and is shown in broken lines. The cylinder head may be the cylinder head  72  for use with the engine  20  as described above with respect to  FIG. 1 . The jackets  100 ,  102 ,  200  are illustrated for use with a cylinder head for a three cylinder, in-line engine with an integrated exhaust manifold in the cylinder head and four overhead valves per cylinder, e.g. two intake and two exhaust valves per cylinder; however, the cooling jacket  200  may be configured for use with other cylinder heads and engine configurations according to the present disclosure. The cooling jackets  100 ,  102 ,  200  are illustrated as cores for forming the cooling passages for each jacket within the cylinder head. Each core represents a negative view of corresponding passages within the head, and may represent the shape of a sand core or lost core used in a casting process for the head. 
     The cylinder head mates with a corresponding cylinder block to provide three cylinders, generally positioned and indicated as I, II, III in  FIG. 2 , and the cylinder head may receive coolant from the cylinder block, as shown in  FIG. 1 . The head provides support for two intake valves for each cylinder that are positioned in region  150  of  FIG. 2  for the associated cylinder. A spark plug for each cylinder is positioned in region  152 . First and second exhaust valves for each cylinder are positioned in regions  154 ,  156 . The head has an integrated exhaust manifold which passages through region  158  which is adjacent to an exhaust face of the head. An exhaust manifold  40  attaches to the exhaust face of the head, as shown in  FIG. 1 . An integrated exhaust manifold provides for exhaust passages or runners formed within the head from the exhaust valves and ports to an exhaust face of the cylinder head where an exhaust manifold, turbocharger, or the like connects. 
     The cooling jacket  200  provides for equivalent cooling of the cylinder head as compared to the conventional jackets  100 ,  102 , but occupies a much smaller volume of the cylinder head. As the volume of the cooling jacket  200  is lower than the conventional jackets  100 ,  102 , the same flow velocity and heat transfer rates may be provided in the cooling jacket  200  using a smaller pump  88 . Similarly, as the volume of the cooling jacket  200  is lower than the conventional jackets  100 ,  102 , a higher flow velocity and heat transfer rates may be provided using the same pump  88 . The cooling jacket  200  only directs coolant to regions of the cylinder head that are hot during engine operation and require cooling. The cooling jacket  200  does not direct coolant to regions of the engine that rise in temperature during engine operation but remain below a specified threshold or below the melting point of the cylinder head material at a maximum engine load and high ambient temperature. 
     The cooling passages of the cooling jacket  200  may be formed with complex shapes and structures, as described herein, and are formed at the time the component or head is cast, molded, or the like as a net shape that generally does not require further machining or processing. The component or cylinder head may be formed from a metal, for example aluminum or an aluminum alloy in a high pressure, near net or net die casting process. In one example, the cooling jacket is formed from or includes a lost core material such as a salt core, a sand core, a glass core, a foam core, or another lost core material as appropriate. 
     The cooling jacket  200  is provided with shapes to minimize flow disturbances. For example, fluid junctions are provided as y-shaped junctions. Fluid passages may have a continuously increasing or decreasing tapering cross section. Turns made by the fluid passages in the cooling jacket are made using a smooth curved structure, and may have no greater than a ninety degree bend, and may include a radius of curvature that is several times larger than a diameter of the passage. The cooling jacket  200  may have slight curves or bends to better package the passages within the constraints of the component. 
     The fluid passages in the cooling jacket  200  may have circular cross sectional shapes or other cross sectional shapes, including elliptical, ovoid, or shapes that include convex and concave regions, e.g. a kidney bean shape, and other regular and irregular shapes. The cross sectional shapes of passages the cooling jacket  200  may generally be the same or may vary at different locations within the jacket compared to one another or within an individual passage. Additionally, the passages within the jacket  200  may have an effective diameter or cross sectional area that increases or decreases in various regions of the insert, for example, as an increasing or decreasing tapered section. Changing cross sectional areas may be provided as gradual, continuous changes, and without any steps or discontinuities, to reduce or minimize flow losses in the fluid circuit. 
     Also note that the cooling jacket  200  may eliminate various plugs or end caps that are present in the conventional cooling jackets  100 ,  102  as illustrated in  FIG. 2 . This improves the integrity of the system  200  by reducing locations where fluid leaks are possible, and further reduces the volume of the cooling jacket, leading to a higher efficiency system. It also increases the manufacturability, as it reduces the number of steps and processes for forming a finished component such as a cylinder head. 
     The cooling jacket  200  has a series of interconnected fluid passages as shown in  FIGS. 3-4  that direct pressurized lubricant to various regions of the cylinder head for thermal management of the cylinder head. The position, shape, and size of the passages are closely controlled based on the present disclosure to control the temperature of the cylinder head during engine operation, and provide an efficient effective cooling jacket. The cooling jacket  200  has passages with various curved shapes and structures, and smooth changes in cross sectional area and direction to provide for reduced flow losses. For example, the overall pressure losses are due to friction, which is a component with two different aspects; one is the major losses caused by an enclosed pipe with a certain length; and the other aspect is local losses which are caused by the bends in the flow path and/or sudden changes in flow area. The local losses are commonly referred to as “K Losses” and are the easier of the two losses to control and reduce an overall pressure loss for the system. 
     By improving the flow characteristics of the cooling jacket  200 , a smaller pump  88  may be used, and the system may operate at a higher efficiency, thereby increasing the engine efficiency, fuel economy, and reducing overall engine parasitic loses. The size, e.g. the diameter of a circular passage or effective diameter for a noncircular cross sectional passage, and the length of the passages affects the pressure, flow rate, and losses within the jacket  200 . Size may also refer to the cross sectional areas of the passages, which is linked to the effective diameter. Likewise, the shape of the passages, e.g. the number of turns or bends in the passages, how tight the turns are, and a change in diameter, affects the pressure, flow rate, and losses in the jacket  200 . A gradual, smooth, or continuous diameter or area change in a passage results in lower flow losses than a discrete or stepwise diameter change. Similarly, a smooth, curved, bend or turn results in lower flow losses than an angled turn or bend with a corner element. 
     Conventional cooling jackets  100 ,  102  are shaped to generally give the coolant whatever is left of the cylinder head volume after the combustion requirements and component positioning requirements are met. After the cooling jackets  100 ,  102  have been associated with the remaining volume of the head, various localized flow and or thermal issues may be addressed using balancing and ribbing techniques or by simply increasing the volumetric flow rate of the pump, for example, by adjusting the blade shape, modifying gearing to increase pump speed, etc. Using the conventional cooling jackets  100 ,  102 , regions of the cylinder head are “overcooled” and other regions of the cylinder head may be in need of more cooling. As engine design changes, for example, by moving to a turbocharged or boosted engine with higher boost pressures, the engine operating temperature will increase, and engine cooling demands also increase. The cooling capacity of the cooling jackets  100 ,  102  may act to limit the engine boost pressures or other engine design characteristics. Additionally, any inefficiencies in the cooling jackets  100 ,  102  may also reduce overall fuel efficiency of the engine, as the pump in the cooling system acts as a parasitic loss for the engine. Additionally, the large passages and volumes of the cooling jackets  100 ,  102  require a longer time to heat up and/or cool down which directly impacts emissions requirements. 
     The cooling jacket  200  provides for directed flow of the coolant by providing an interconnected network of cooling passages with the size of the passages varied to reduce or minimize flow losses through the jacket  200  and supply the a higher or maximized flow velocity to area of the cylinder head with a high heat load, or the critical areas, while generally areas of the cylinder head with a low operating temperature and a low heat load. The jacket  200  is provided with a network of interconnected passages that are positioned to distribute the flow in an even manner to the high priority heat flux locations first. The shapes and sizes of the passages in the jacket  200  may be varied based on the structure of the associated cylinder head, the head flux of the associated head and engine, and various manufacturing limitations. As a result the cooling jacket  200  provides colder and faster coolant to regions with higher operating temperatures, thus improving the efficiency of the jacket  200  and overall cooling system. The passages in the jacket  200  may be generally sized to have a narrow or small diameter, for example, with a length to diameter ratio of the passages being more than three, more than five, or more than ten in various examples. 
     The overall volume of the cooling jacket  200  is greatly decreased from the jackets  100 ,  102 . As the passages in the jacket  200  are reduced or minimized in volume, the overall volume of the jacket  200  is reduced, and the warm-up/cooldown times for the head are also reduced. 
     Likewise, as the volume of the jacket  200  is smaller, the pump for the cooling system has a reduced demand, and will therefore require less power to operate and provide increased system efficiency. 
     The various passages of the jacket  200  are sized to provide sufficient cooling to high temperature regions of the cylinder head during engine operation. Similarly, to prevent issues such as a vapor phase change of the coolant in the passages of the jacket  200 , for example, after engine or vehicle shut down, a secondary electric coolant pump  89  may be provided to circulate coolant post-shut down and prevent a phase change. The coolant pump  89  may be arranged sequentially with the pump  88  for serial flow, or may be arranged for parallel flow with the pump  88  as shown in  FIG. 1 . 
       FIGS. 3-4  illustrate perspective view of the cooling jacket  200  according to the present disclosure and as shown in  FIG. 2 .  FIG. 5  illustrates a schematic view of the cooling jacket of  FIGS. 3-4 . The “S”, “M”, and “B” indicate the sizes of similar elements relative to one another, with S referring to the smallest size, M referring to a medium or intermediate size, and B referring to the biggest or largest size. When more than three passages are provided in a set of similar elements, the relative size trend may remain the same, with the passages arranged largest to smallest, or vice versa, relative to one another. 
     The jacket  200  has a first main passage  202 , and a second main passage  204 . Each passage  202 ,  204  extends generally along or parallel to a longitudinal axis  226  of the engine. The passage  202  may be an inlet passage and is generally associated with cooling the spark plug regions  152  of the cylinder head. The passage  204  may be an outlet passage and is generally associated with cooling the exhaust valve regions  154  and exhaust valve bridges between adjacent valves in the cylinder head. The first and second passages are connected by an integrated exhaust manifold (IEM) cooling passage  206  that is associated with cooling the region  158  surrounding the IEM and the exhaust face of the head. The first passage  202  receives coolant from coolant feed passages fluidly connected to the cooling jacket  84  in the cylinder block. The second passage  204  provides coolant to a coolant outlet for the head, which in turn flows to a pump, radiator, or other component in the cooling system  80 . 
     The inlet passage  202  receives at least one coolant feed, and in the present example, receives coolant feeds at four longitudinal locations of the engine. The block cooling jacket  84  may be provided in an open deck, semi-open deck or closed deck engine, and apertures are provided as appropriate in the block deck face and/or head gasket to provide the flow of coolant from the block to the head jacket  200 . In the present example, the inlet passage  202  receives a feed of coolant via first and second feed passages  208 ,  210  at a first end  212  of the engine from a cooling jacket in the block. The inlet passage  202  receives another feed of coolant via third and fourth feed passages  214   216 , yet another feed of coolant at fifth and sixth feed passages  218 ,  220 , and a final seventh coolant feed  222  at the opposed end  224  of the engine, such that coolant generally flows from right to left through passage  202  in  FIG. 3 . Passage  222  may be larger in cross sectional area than what is shown in  FIG. 3 , flow through passage  222  may be restricted via use of an orifice, e.g. using the head gasket, or may not be present in the jacket  200 . Flow through any of the feed passages may be restricted at the inlet to the respective feed passage via use of an orifice, e.g. an orifice in the head gasket. 
     In the present example, the feed passages at each longitudinal location of the head are on either side of the main longitudinal axis  226  of the engine. In other examples, only one feed passage may be provided at a longitudinal location in the engine, or more than two feeds may be provided. In the present example, the coolant in the underlying engine block cooling jacket flows from end  224  of the engine to the other end  212  of the engine. In other examples, the coolant in the underlying engine block may flow in the opposite direction, or in another flow pattern. 
     The cooling jacket  200  also has an inlet valve cooling passage  228  associated with each pair of inlet valves that connects to an associated feed passage. In other examples, the jacket  200  may not have inlet valve cooling passages  228 . The inlet valve passage  228  is only illustrated in  FIGS. 3-4  for clarity of  FIG. 5 . The inlet cooling passage  228  may be provided to provide a low coolant flow or relief from a region of the block jacket and may not provide a significant impact on the head jacket  200  flow. Passages  228  may have various sizes, and may be larger in cross sectional area than what is shown in  FIG. 3 . Alternatively, flow through passage  228  may be restricted via use of an orifice. 
     Each feed passage  208 - 222  has a smaller cross sectional area than the preceding upstream feed passage. The cross sectional area of an individual feed passage increases in cross sectional area along the length of the feed passage to provide for smooth entry and mixing of the coolant in the feed passage with the coolant in the inlet passage. The feed passages at each longitudinal location may have equivalent cross sectional areas and general shapes compared to one another, or may differ in area and/or shape. In the present example, feed passages passage  208  has a larger cross sectional area than downstream feed passage  214 , which in turn has a larger cross sectional area than downstream feed passage  218 , which has a larger cross sectional area than feed passage  222 . 
     The inlet passage  202  itself continually decreases in cross sectional area along the length of the passage  202  and in the direction of coolant flow therethrough. The passage  202  incorporates annular passage regions  230 ,  232 ,  234  to provide coolant flow around a spark plug. The annular passage region may have an equivalent cross sectional area as the section of the inlet passage  202  immediately preceding the annular passage region. The present example has three annular passage regions, with decreasing cross sectional area corresponding to the decreasing cross sectional area of the overall inlet passage  202 . Annular passage region  230  has a larger cross sectional area than downstream annular passage region  232 , which in turn has a larger cross sectional area compared with downstream annular passage region  234 . 
     Coolant flow leaves the inlet passage  202  at each annular passage region  230 ,  232 ,  234  through a respective lower passage  236 ,  238 ,  240  in a series of lower passages. Each lower passage  236 ,  238 ,  240  fluidly connects a respective annular passage region of the inlet passage  202  with the IEM cooling passage  206 . Each lower passage  236 ,  238 ,  240  has a larger cross sectional area compared to a preceding upstream lower passage. In the present example, lower passage  236  has a smaller cross sectional area than lower passage  238 , which in turn has a smaller cross sectional area than passage  240 . The cross sectional area of an individual lower passage may increase along the length of the lower passage. Each lower passage may generally follow and be below an exhaust runner or passage of the engine to assist in cooling the cylinder head adjacent to the exhaust passage. 
     The IEM cooling passage  206  provides a passage to surround the exhaust passages adjacent to the exhaust face of the cylinder head defined as region  158 . Without cooling, the exhaust face of the cylinder head may reach a high temperature during engine operation as exhaust components are connected to the face, and heat loss to the ambient environment is therefore limited. 
     The coolant leaves the IEM passage  206  through upper passages  246 ,  248 ,  250 . The coolant flows through the IEM passage  206  from the lower passages to the upper passages via a first section  242  or a second section  244  of the IEM passage. In the present example, upper passages  246 ,  248 ,  250  join one another and merge to provide a single fluid connection to the IEM passage  206 . The IEM cooling passage  206  has a cross sectional area that matches or is slightly larger than the cross sectional area of the exit of the lower passage  240 , and in one example this yields a cross sectional area about half of the area depicted at the  240  exit and is a based on the IEM passage  206  being a circular shaped passage where flow may proceed through two separate paths on the circle shaped passage  206  to the three possible exits  246 ,  248 , and  250 . 
     Each upper passage  246 ,  248 ,  250  fluidly connects the IEM passage  206  to the second outlet passage  204  at various locations along the outlet passage  204  with respect to the longitudinal axis  226  of the engine as described below. Each upper passage  246 ,  248 ,  250  has a larger cross sectional area compared to a subsequent downstream upper passage. In the present example, upper passage  246  has a larger cross sectional area than upper passage  248 , which in turn has a larger cross sectional area than passage  250 . The cross sectional area of an individual upper passage may decrease along the length of the upper passage. Each upper passage may generally follow and be above an exhaust runner or passage of the engine to assist in cooling the cylinder head adjacent to the exhaust passage. 
     The second passage or outlet passage  204  itself continually increases in cross sectional area along the length of the passage  204  and in the direction of coolant flow therethrough. The passage  204  incorporates exhaust valve regions  252 ,  254 ,  256  for cooling the cylinder head adjacent to each pair of exhaust valves. Each exhaust valve region has a first annular region  258  and a second annular region  260  surrounding each exhaust valve for a cylinder to provide a pair of annular regions. A bridge region  262  connects the pair of annular regions  258 ,  260  and provides for flow of coolant directly through or across an exhaust bridge in the cylinder. Without sufficient cooling, the exhaust bridge may reach high operating temperatures based on the proximity to the exhaust region of the combustion chamber, being positioned between the two exhaust valves and ports. Exhaust valve regions  254 ,  256  have a similar structure compared to that described with respect to region  252 . 
     Each exhaust valve region may have an equivalent cross sectional area as the section of the outlet passage  204  immediately preceding the exhaust valve region. The present example has three exhaust valve passage regions, with increasing cross sectional area corresponding to the increasing cross sectional area of the overall outlet passage  204 . Exhaust valve region  252  has a smaller cross sectional area than downstream exhaust valve region  254 , which in turn has a smaller cross sectional area compared with downstream exhaust valve region  256 . 
     Each upper passage  246 - 250  may connect to the outlet passage  204  just before each of the exhaust valve regions in one example. In other examples, the upper passages may connect to the exhaust valve regions, for example an annular region, of the outlet passage. 
     The cooling jacket  200  has a single outlet or exit port  264  from the outlet passage  204 . In other examples, the cooling jacket  200  may have more than one outlet. Passage  266  provides a degas line for the cooling jacket  200  and is generally positioned at a high point of the cooling jacket  200  in the cylinder head. Passage  266  may have various sizes, and may be larger or smaller in cross sectional area than what is shown in  FIG. 3 . Alternatively, flow through passage  266  may be restricted via use of an orifice, or may not be present in the jacket  200  if the jacket has an alternative degas strategy. 
     The coolant in the inlet and outlet passages  202 ,  204  flows in opposed directions, and generally longitudinally in the cylinder head and engine. In other examples, the coolant may flow in the same direction in the inlet and outlet passages  202 ,  204 ; however, the cross sectional areas of the upper passages would be generally reversed. 
     As can be seen in  FIGS. 3-4 , each passage of the jacket  200  provides a smooth curved flow path for the coolant, without flow disturbances, abrupt restrictions, or severe bends or corners, and the passages are joined at junctions or intersections that are also smooth, curved, and continuous. As such, losses in the jacket  200  are reduced and flow and cooling efficiencies are increased. 
     Similarly, each passage in the jacket  200  provides a continuously changing cross sectional area. The inlet passage  202  decreases in area, and the outlet passage  204  increases in area with fluid flow. Cross flow passages connecting to the inlet or outlet passage vary in cross sectional area compared to one another. A cross flow passage may be an upper passage or a lower passage in the present example. For example, the cross sectional area of a cross flow passage in a series of cross flow passages increases with a decreasing cross sectional area of the corresponding inlet or outlet passage. 
     Another cooling jacket  300  according to the present disclosure is illustrated schematically in  FIG. 6 . Elements that are the same or similar to those illustrated in  FIGS. 3-5  are given the same reference number. The “S”, “M”, and “B” indicate the sizes of similar elements relative to one another, with S referring to the smallest, M referring to the medium or middle size, and B referring to the largest.  FIG. 6  promotes parallel flow paths and the overall conceptual layout is intact, e.g. it has more of a spider web aspect, which may provide for increased and improved cooling and thermal management of the head. 
     The first passage  204  of the jacket  300  is fed by three feed passages  302 ,  304 ,  306 . Each of the three feed passages is in fluid communication with a coolant source, for example, a block jacket  84 . The feed passages  302 ,  304 ,  306  each are fluidly coupled to a respective annular region  230 ,  232 ,  234  of the passage  202 , opposed to upstream of an annular passage as shown in  FIG. 5 . 
     The lower series of passages  236 ,  238 ,  240  may be coupled to the first passage  202  downstream of the annular regions  230 ,  232 ,  234 , and may join or merge together prior to the fluid coupling with IEM passage  206 . The upper passages  246 ,  248 ,  250  and the second passage  104  with the annular exhaust valve regions  252 ,  254 ,  256  may be arranged in a similar manner as to that described above with respect to  FIGS. 3-5 . 
     Another cooling jacket  400  according to the present disclosure is illustrated schematically in  FIG. 7 . Elements that are the same or similar to those illustrated in  FIGS. 3-5  are given the same reference number. The “S”, “M”, and “B” indicate the sizes of similar elements relative to one another, with S referring to the smallest, M referring to the medium or middle size, and B referring to the largest. In  FIG. 7 , the exhaust valve regions  154 ,  156  are given a higher priority in the cooling path in the jacket compared to the earlier described jackets. 
     A primary feed  402  provides coolant to the first passage  202  and annular regions  230 ,  232 ,  234  surrounding the spark plugs. Each annular region of the first passage  202  may also receive a feed  403 ,  404 ,  406 , for example, from a block cooling jacket. A first series of passages  408 - 418  fluidly couple the annular regions of the first passage  202  to the IEM passage  206 , which may have a non-uniform cross-sectional area as shown. The coolant exits the IEM passage  206  through passage  420 , which couples with a coolant outlet  422 . 
     A second series of passages  424 - 428  fluidly couples the first passage  202  to the second passage  204 . The second passage includes annular regions  252 ,  254 ,  256  for cooling of the exhaust valves. Coolant exits the fluid passage  204  via passage  430 . Passage  430  merges with passage  420  prior to the coolant outlet  422 . As can be seen from  FIG. 7 , coolant is directed first to cool the spark plug regions of the head, and then is divided in a split parallel flow configuration to direct the coolant to both the IEM region and the exhaust valve regions of the head. 
     Generally, the cooling jacket may be sized according to the following general principles. Of course, deviations from this may be required, for example, due to packaging constraints and the like imposed by the overall structure and other systems in the cylinder head. The inlet passage continually decreases in cross-sectional area, while the outlet passage continually increases in cross sectional area. The cross flow passages connecting the inlet and outlet passage vary in cross sectional compared to one another, with the first passage providing flow from the inlet passage to the outlet passage having a smaller cross sectional area than the last passage providing flow from the inlet passage to the outlet passage. The cross sectional area of the inlet and the outlet of the cooling jacket are generally equal to one another, or the outlet cross sectional area is larger than the inlet cross sectional area. The cross sectional area of the system at various stages in the system remains a generally constant value, as explained below. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosure. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the disclosure.