Abstract:
A cast cylinder head for an internal combustion engine. The cylinder head includes a first surface, a rear surface, and an intake passageway. The first surface is adapted to be connected to a cylinder housing, and the rear surface extends from the first surface. The intake passageway is in the cylinder head and extends from an inlet on the rear surface toward an outlet on the first surface. The intake passageway includes a straight portion that extends from the rear surface and that includes an axis. The included angle between the axis and the first surface is approximately thirty-five to forty-five degrees.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to cylinder heads for internal combustion engines, and more particularly to die cast cylinder heads for internal combustion engines.  
         BACKGROUND OF THE INVENTION  
         [0002]    Known piston-type internal combustion engines generally include a cylinder housing, a cylinder head, and a cylinder head cover as well as a crankcase. The cylinder head encloses a combustion chamber that is defined at the end of the cylinder housing. Some cylinder heads and cylinder head covers include a cam shaft and rocker arm assembly that is driven by a crankshaft to operate intake and exhaust valves to feed a air/fuel mixture to the combustion chamber and to exhaust combustion gases from the combustion chamber.  
           [0003]    Typically, high-speed, high-output cylinder heads are manufactured by a gravity casting process that utilizes sand or degradable cores to create internal coring of the cylinder head. For example, the degradable cores are used to make smoothly curved intake and exhaust ports that communicate with the intake and exhaust valves. The smooth curves in the intake and exhaust ports are important for unrestricted fluid flow and efficient operation of the engine. Specifically, the intake port must be properly configured to maximize power and to create the correct charge motion of the air/fuel mixture in the combustion chamber to increase fuel economy and improve emissions.  
           [0004]    Die casting cylinder heads provides a significant cost savings in the manufacture of cylinder heads. But historically die casting of cylinder heads has been disadvantageous because of the inability of the process to successfully core the intake and exhaust ports to a configuration which is necessary to obtain comparable engine efficiencies. In addition, tools used to die cast cylinder heads for use with overhead cams have been limited to casting only a single cylinder head per casting cycle. These tools have been incapable of die casting multiple cylinder heads per cycle because the contour of the cylinder head has required movable slides on all sides.  
         SUMMARY OF THE INVENTION  
         [0005]    The die cast cylinder head of the present invention decreases the manufacturing costs of the cylinder head by coring the intake and exhaust ports to a substantially finished configuration during the die casting operation. Further, the die cast intake port is angled 40 degrees and the die cast exhaust port is parallel to the base plane of the cylinder head. The die cast ports are operable on high-speed, high-output, single cylinder engines of the type typically used on two wheeled motorized vehicles.  
           [0006]    In addition, the cost to manufacture the die cast cylinder head is decreased because the cylinder head is configured to allow multiple cavities within a single tool. Specifically, one side of the cylinder head is contoured such that it can be formed by the separating halves of the tool without the need for independent slides. Since no slide is necessary on one side of the cylinder head, two cavities can be manufactured into the tool by positioning the cylinder heads such that the sides that do not require a slide are adjacent to each other.  
           [0007]    One embodiment of the present invention includes a cast cylinder head for an internal combustion engine. The cylinder head includes a first surface, a rear surface, and an intake passageway. The first surface is adapted to be connected to a cylinder housing, and the rear surface extends from the first surface. The intake passageway is in the cylinder head and extends from an inlet on the rear surface toward an outlet on the first surface. The intake passageway includes a straight portion that extends from the rear surface and that includes an axis. The included angle between the axis and the first surface is approximately thirty-five to forty-five degrees.  
           [0008]    Another embodiment of the invention includes a cylinder head assembly for an internal combustion engine. The cylinder head assembly includes a cylinder head, a cylinder head cover, a first bearing, a second bearing, and a cam shaft. The cylinder head includes first and second bearing supports. The cylinder head cover is coupled to the cylinder head and includes third and fourth bearing supports. The first bearing is supported by the first bearing support and the third bearing support, and the second bearing is supported by the second bearing support and the fourth bearing support. The cam shaft includes a first portion that is rotatably mounted within the first bearing and a second portion that is rotatably mounted within the second bearing.  
           [0009]    Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a side view illustrating an engine/transmission assembly including a cylinder head embodying the present invention.  
         [0011]    [0011]FIG. 2 is a cross section view taken along line  2 - 2  in FIG. 1.  
         [0012]    [0012]FIG. 3 is a cross section view taken along line  3 - 3  in FIG. 2.  
         [0013]    [0013]FIG. 4 is a partial cross section view taken along line  4 - 4  in FIG. 2.  
         [0014]    FIGS.  5 - 7  are schematic representations of two cylinder heads which are capable of being produced using one die tool and one die casting machine.  
         [0015]    [0015]FIG. 8 is a cross section view of the cylinder head shown in FIG. 1, illustrating the cylinder head in the “as cast” condition.  
         [0016]    [0016]FIG. 9 is a view similar to FIG. 8, illustrating the intake and exhaust ports of the cylinder head after machining. 
     
    
       [0017]    Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of “consisting of” and variations thereof herein is meant to encompass only the items listed thereafter. The use of letters to identify elements of a method or process is simply for identification and is not meant to indicate that the elements should be performed in a particular order.  
       DETAILED DESCRIPTION  
       [0018]    [0018]FIG. 1 illustrates an engine/transmission assembly  10  that includes an internal combustion engine  12  having a crankcase  14 . The engine  12  includes a cylinder housing  16  connected to the forward portion of the crankcase  14 , a cylinder head  18  connected to the cylinder housing  16 , and a cylinder head cover  20  connected to the cylinder head  18 . The cylinder head cover  20 , the cylinder head  18 , the cylinder housing  16 , and the crankcase  14  are connected with elongated studs  22  that extend from the crankcase  14  through holes  24  located near the outer surfaces of the cylinder housing  16 , the cylinder head  18 , and the cylinder head cover  20  (FIG. 4).  
         [0019]    Referring to FIGS.  2 - 4 , the cylinder head  18  includes a top or first surface  26 , a bottom or second surface  28 , a front face  30 , a rear face  32 , and first and second side faces  34 ,  36 . The cylinder head  18  is fastened to the cylinder housing  16  such that a gasket  38  is coupled between a planar portion  40  of the bottom surface  28  and a corresponding planar portion  42  of the cylinder housing  16 . The planar portion  40  of the bottom surface  28  defines a base plane  44 . The cylinder head  18  is fastened to the cylinder head cover  20  such that a planar portion  46  of the top surface  26  of the cylinder head  18  is in contact with a corresponding planar portion  48  of the cylinder head cover  20 .  
         [0020]    Referring specifically to FIG. 3, the cylinder head  18  further includes an intake port  50  that extends through the cylinder head  18  from the rear face  32  to the bottom surface  28  to communicate with a combustion chamber  51 . The intake port  50  includes a straight portion  52  that projects downwardly from the rear face  32  and a curved portion  54  that smoothly transitions from the straight portion  52  to the bottom surface  28  and the intake valve seat  74 . The curved portion  54  is preferred, but is not necessarily required. The straight portion  52  projects downwardly from the rear face  32  at approximately an angle θ relative to the base plane  44 . Angle θ is the included angle between a longitudinal axis  53  of the straight portion  52  and the base plane  44 . The angle θ is preferably between 35 to 45 degrees, and more preferably the angle θ is approximately 40 degrees. The straight portion  52  and curved portion  54  are shaped to provide optimum air flow to the cylinder housing  16  for increased power and responsiveness. The intake port  50  directs the flow in a manner that creates a proper charge motion inside the cylinder housing  16  for increased fuel economy and improved emissions.  
         [0021]    The configuration of the intake port  50  is important because it allows the cylinder head  18  to be die cast and provides the proper flow characteristics necessary for power and efficient operation of the engine  12 . The straight portion  52  of the intake port  50  can be die cast because the straight portion  52  of the intake port  50  does not require loose cores and can be formed with straight pulling cores. In addition, the critical flow characteristics are maintained by angling the straight portion  52  of the intake port  50  between 35 and 45 degrees.  
         [0022]    The cylinder head  18  further includes an exhaust port  56  that extends through the cylinder head  18  from the front face  30  to the bottom surface  28  to communicate with the combustion chamber  51 . The exhaust port  56  also includes a straight portion  58  that projects inwardly from the front face  30  and a curved portion  60  that smoothly transitions from the straight portion  58  to the bottom surface  28  and the exhaust seat  76 . The straight portion  58  includes a longitudinal axis  59  that is approximately parallel to the base plane  44 . The straight portion  58  and the curved portion  60  are configured to reduce the restriction of exhaust gases flowing from the cylinder housing  16  to reduce heat transfer into the cylinder head  18 .  
         [0023]    The configuration of the exhaust port  56  is substantially less critical to engine performance compared to the configuration of the intake port  50 . Since the angle of the exhaust port  56  is not a critical factor, the longitudinal axis  59  of the straight portion  58  of the exhaust port  56  is parallel to the base plane  44  to simplify the die casting process. The casting process is simplified because the straight portion  58  can be formed by the slide of the tool that forms the front face  30  of the cylinder head  18  such that a retractable core similar to the one that forms the straight portion  52  of the intake port  50  is not necessary.  
         [0024]    As shown in FIG. 4, the cylinder head  18  further includes a cooling passage  62  that includes first and second portions  64 ,  66 . The first portion  64  extends rearwardly from the front face  30  though a substantial portion of the cylinder head  18 . The second portion  66  extends from the second side face  36  and connects with the first portion  64  such that air is allowed to pass through the first and second portions  64 ,  66  to cool the cylinder head  18 . An additional feature of these two passages is that they are shaped to remove a substantial amount of casting material to reduce shrinkage and to improve the life of the tool  170 . The boss for stud  22  is partially removed to allow a die casting slide to be retracted (FIG. 4).  
         [0025]    Referring back to FIG. 3, the engine  12  includes a valve train  68  that includes an intake valve  70  and an exhaust valve  72 . The intake valve  70  includes a longitudinal axis  71  that defines an included angle γ between the longitudinal axis  71  and the base plane  44 . The angle γ is preferably between 72 to 82 degrees, and more preferably the angle γ is approximately 77 degrees. The exhaust valve  72  includes a longitudinal axis  73  that defines an included angle δ between the longitudinal axis  73  and the base plane  44 . The angle δ is preferably between 58 to 80 degrees, and more preferably the angle δ is approximately 74 degrees. The cylinder head  18  includes first and second valve seats  74 ,  76  that encircle the intake and exhaust ports  50 ,  56 , respectively, adjacent to the bottom surface  28 . The intake valve  70  extends through a first valve bushing  78  and the intake port  50  such that a head  80  of the intake valve  70  is biased upward against the first valve seat  74 . The exhaust valve  72  extends through a second valve bushing  82  and the exhaust port  56  such that a head  84  of the exhaust valve  72  is biased upward against the second valve seat  76 .  
         [0026]    As shown in FIGS. 2 and 4, the top surface  26  of the cylinder head  18  includes first and second lower bearing supports  86 ,  88 . Each of the bearing supports  86 ,  88  is semi-circular and includes a centrally positioned annular groove  90 . The cylinder head  18  includes a lubricant passage  92  that extends from the stud hole  24  to the annular groove  90  of the first lower bearing support  86  (FIG. 4). The top surface  26  also includes a slot  94  that is positioned between the lower bearing supports  86 ,  88  (FIGS. 2 and 3).  
         [0027]    As best shown in FIGS. 6 and 7, the front face  30  includes a plurality of forwardly extending horizontal cooling fins  96  that partially wrap around the corner of the cylinder head  18  to cover a portion of the second side face  36 . The first side face  34  is angled by a draft angle α relative to a vertical axis  98  that is perpendicular to the base plane  44 . The second side face  36  includes a plurality of forwardly extending horizontal cooling fins  100 . The rear face  32  includes a plurality of rearwardly extending vertical cooling fins  102 . Cooling fins have been historically positioned so that they are all parallel to the direction of cooling air flow. The cooling fins  96 ,  100  on the front and side faces  30 ,  36  are transverse to the cooling fins  102  on the rear face  32 . Although the direction of the fins  96 ,  100 ,  102  is varied, the fins  96 ,  100 ,  102  remove a sufficient amount of heat from the cylinder head  18  compared to fins that are all aligned in the same direction. The vertical fins  102  of the rear face  32  and the draft angle α of the first side face  34  provide a tooling advantage which will be explained in more detail below. In addition, the fins  96 ,  100 ,  102  allows the engine  12  to be cooled by a natural draft when the engine  12  is exposed and allows the engine  12  to be fan cooled when the engine  12  is enclosed within a cover (not shown) such as on a scooter, for example.  
         [0028]    Referring again to FIGS. 2 and 4, the cylinder head cover  20  includes a bottom surface  104 . The bottom surface  104  includes first and second upper bearing supports  106 ,  108 . Each of the bearing supports  106 ,  108  is semi-circular and includes a centrally positioned annular groove  110 . The cylinder head cover  20  also includes a rocker shaft bore  112  that extends from a side of the cylinder head cover  20  toward the opposite side of the cylinder head cover  20 . The rocker shaft bore  112  includes a threaded portion  114  adjacent to the opening of the rocker shaft bore  112  and a proximate portion  116  that is adjacent to the threaded portion  114 . The rocker shaft bore  112  also includes a distal portion  118  that has a diameter that is smaller than the diameter of the proximate portion  116 . The cylinder head cover  20  includes a first lubricant passage  120  that fluidly connects the annular cavity of the first upper bearing support  106  to the distal portion  118  of the bore  112 , and a second lubricant passage  122  that fluidly connects the annular cavity of the second upper bearing support  108  to the proximate portion  116  of the bore  112 .  
         [0029]    The engine  12  includes a hollow rocker shaft  124  that is inserted into the rocker shaft bore  112 . The rocker shaft  124  includes a shaft portion  126  and a head portion  128 . The rocker shaft  124  includes a first lubricant opening  130  on the distal end of the shaft portion  126  and a second lubricant opening  132  on the proximate end of the head portion  128 . The shaft portion  126  is positioned within the distal portion  118  of the rocker shaft bore  112  and the first lubricant opening  130  is in fluid communication with the first lubricant passage  120 . The head portion  128  is positioned within the proximate portion  116  of the rocker shaft bore  112  and the second lubricant opening  132  is in fluid communication with the second lubricant passage  122 . An insert  134  is positioned in the first lubricant passage  120  and through the first lubricant opening  130  to align the lubrication openings  130 ,  132 ,  144  and prevent the rotation of the rocker shaft  124 . A threaded plug  136  and wave washer  135  are inserted into the threaded portion  114  of the rocker shaft bore  112  to maintain the rocker shaft  124  within the rocker shaft bore  112  and to locate it inwardly against the end of the bore  118  so that end play of the rocker arms  138  can be controlled.  
         [0030]    The engine  12  also includes rocker arms  138  that are pivotably connected to the shaft portion  126  of the rocker shaft  124  between a facing  140  on the cylinder head cover  20  and the head portion  128  of the rocker shaft  124 . The rocker arms  138  are coupled to respective valves  70 ,  72  and include lubrication holes  142  (FIGS. 2 and 3). The lubrication holes  142  of the rocker arms  138  align with lubrication holes  144  of the rocker shaft  124  when the rocker arms  138  are in a specific angular position relative to the rocker shaft  124  (FIG. 3).  
         [0031]    With reference to FIGS. 2 and 4, the engine  12  further includes first and second cam bearings  146 ,  148  that include annular grooves  150  that are centrally located on the outside diameter of the cam bearings  146 ,  148 . Each cam bearing  146 ,  148  includes an annular ring  152  that is biased within the annular groove  150  of the cam bearing  146 ,  148 . The first cam bearing  146  is coupled between the first lower and upper bearing supports  86 ,  106  and the second cam bearing  148  is coupled between the second lower and upper bearing supports  88 ,  108  such that the annular ring  152  is positioned within the annular grooves  90 ,  110  of the upper and lower bearing supports  86 ,  88 ,  106 ,  108 . The annular rings  152  axially locate the cam bearings  146 ,  148  with respect to the upper and lower bearing supports  86 ,  88 ,  106 ,  108  and prevent axial movement of the cam bearings  146 ,  148 . An additional feature of the annular grooves  90 ,  110  is that they reduce casting material. Rectangular pockets  153  are added to the grooves to further reduce the amount of casting material to reduce shrinkage and improve the life of the tool  170  (FIGS. 2 and 4).  
         [0032]    The engine  12  also includes a cam shaft  154  that is inserted within and rotatably coupled to the first and second cam bearings  146 ,  148 . The cam shaft  154  includes lobes  156  that slidably engage the rocker arms  138  such that rotation of the cam shaft  154  pivots the rocker arms  138  and moves the intake and exhaust valves  70 ,  72 . As illustrated in FIGS. 2 and 3, the cam shaft  154  is prevented from axial movement by a key  160  that is inserted in the slot  94  of the cylinder head  18 . The key  160  extends upward into an annular groove  162  in the cam shaft  154  between the cam lobes  156 . The key is a loose piece and is not fastened in place with a fastener, but instead is maintained in position by the annular groove  162  of the cam shaft  154  and the slot  94  of the cylinder head  18 .  
         [0033]    The lubrication of the cylinder head  18  and cylinder head cover  20  is described with reference to FIGS. 2 and 4. A pump (not shown), pumps a lubricant from the crankcase  14  up through the cylinder head  18  by forcing lubricant through a clearance between the stud  22  and stud hole  24 . Once the lubricant reaches the cylinder head  18 , the lubricant flows through the lubricant passage  92  and into the annular grooves  90 ,  110  to lubricate the cam shaft  154  through a hole  164  in the first cam bearing  146 . From the annular grooves  90 ,  110 , the lubricant flows through the first lubrication opening  130  and into the hollow rocker shaft  124 . The lubricant in the hollow rocker shaft  124  intermittently lubricates the rocker arms  138  and cam lobes  156  through the lubrication holes  142 ,  144  when the rocker arms  138  are in a specific position relative to the rocker shaft  124 . The remaining lubricant in the rocker shaft  124  flows across the rocker shaft  124 , through the second lubrication opening  132  and lubrication passage  122  and into the annular grooves  90 ,  110  to lubricate the cam shaft  154  through a hole (not shown) in the second cam bearing  148 . After the lubricant is diverted throughout the cylinder head  18 , it accumulates on the top surface  26  of the cylinder head  18  until it overflows into a chain cavity  168  of the cylinder head  18  and down the chain cavity  168  into the crankcase  14 .  
         [0034]    Although the bearings  146 ,  148  may rotate within the bearing supports  86 ,  88 ,  106 ,  108 , the cam shaft  154  continues to be properly lubricated because the lubricant flows throughout the annular grooves  90 ,  110  and therefore the angular position of the cam bearing holes  164  is not critical.  
         [0035]    The cylinder head  18  is die cast, and is capable of being die cast in a two cavity tool  170  as shown in FIG. 5. FIG. 5 illustrates a stationary side  172  of the tool  170  with two die cast cylinder heads  18  positioned within the tool  170 . As shown in FIG. 8 the stationary side  172  of the tool  170  forms the cast shape of the bottom surface  28  of the cylinder head  18  including portions of the intake and exhaust ports  50 ,  56 .  
         [0036]    Referring to FIGS.  6 - 7 , the tool  170  includes an ejector side  174  that mates with and that is movable with respect to the stationary side  172  of the tool  170 . The ejector side  174  forms the cast shape of the top surface  26  of the cylinder head  18  including the chain cavity  168 , first and second lower bearing supports  86 ,  88 , and the annular grooves  90 . The ejector side  174  of the tool  170  also includes a core  176  that is moveable with the ejector side  174  of the tool  170 . The core  176  is extendable to form the straight portion  52  of the intake port  50  (FIG. 8) and retractable such that the cast cylinder head  18  can be removed from the tool  170 .  
         [0037]    As shown in FIGS.  5 - 7 , the front face  30  of the cylinder head  18  is created by a first slide  178  and the second side face  36  is created by a second slide  180 . The first slide  178  forms the horizontal fins  96 , the straight portion  58  of the exhaust port  56 , and the first portion  64  of the cooling passage  62 . The second slide  180  forms the horizontal fins  100  and the second portion  66  of the cooling passage  62 .  
         [0038]    The rear face  32  of the cylinder head  18  does not use a slide to form the fins  102  and contour. Instead, the vertical fins  102  of the rear face  32  are capable of being formed by the stationary side  172  of the tool  170 , and therefore no slide is necessary which would otherwise interfere with the operation of the core  176  that forms the straight portion  52  of the intake port. In other words, the contour and fins  102  of the rear face  32  are capable of being formed by a coreless tool. The portions of the rear face  32  which are created by the stationary side  172  of the tool  170  are angled relative to the vertical axis  98  by the draft angle α. As shown in FIGS. 6 and 7, the draft angle α is approximately 2 degrees relative to the vertical axis  98 . The draft angle α can be as small as 0.5 degrees while still allowing the cast cylinder head  18  to be removed easily from the tool  170 .  
         [0039]    The first side face  34  of the cylinder head  18  is formed without the use of slides or cores (i.e., with a coreless tool). Rather, the first side face  34  is formed by the stationary and ejector sides  172 ,  174  of the tool  170 . Because the first side face  34  is formed without using slides, the tool  170  is capable of having two cavities that are 180 degrees relative to each other so that the tool  170  can cast two cylinder heads  18  in the same cycle. Specifically, the first side face  34  of a first cast cylinder head  18  is positioned adjacent to the first side face  34  of a second cast cylinder head  18 . In contrast, if all of the faces  30 ,  32 ,  34 ,  36  required slides, the equipment used to actuate the slides would prevent multiple cavities from being positioned together because the slides of one cavity would interfere with the slides of the adjacent cavity.  
         [0040]    The cast shape of the cylinder head  18  is illustrated in FIG. 8. The intake and exhaust ports  50 ,  56  are cast with dividers  182  that allow casting alloy to flow therethrough. The cast shape is a near net cast shape which requires only minor machining where tolerances are critical. This is a significant cost savings because less material needs to be removed during machining operations. In addition, where the tolerances are not critical, the features of the cylinder head  18  need not be machined at all and can be utilized in the cast condition.  
         [0041]    [0041]FIG. 9 illustrates machined intake and exhaust ports  50 ,  56  of the cylinder head  18  with the intake and exhaust ports  50 ,  56  in their final operable form. The machining involves plunging a ball end mill through the dividers  182  to open the intake and exhaust ports  50 ,  56 . This machining step leaves sharp comers  184  on the interior bend where the straight portion  52 ,  58  transitions into the curved portions  54 ,  60 . The sharp corner  184  on the intake port  50  can prevent the charge from correctly flowing into the cylinder housing  16 , and the sharp comer  184  on the exhaust port  56  increases heat transfer to the cylinder head  18  and restricts the flow of the exhaust gases. Additional precision machining removes the sharp corners  184  from the intake and exhaust ports  50 ,  56  to improve the efficiency of the engine  12 , to improve the flow characteristics of the intake and exhaust ports  50 ,  56 , and to reduce the operating temperature of the cylinder head  18  charge and the exhaust gases.