Patent Publication Number: US-2004050366-A1

Title: Fuel injector mounting construction for engine

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] This invention relates to a fuel injector mounting construction for an in internal combustion engine, and more particularly to an improved fuel injector mounting construction on a direct injected engine that can securely hold a fuel injector notwithstanding manufacturing tolerances.  
       [0003] 2. Description of Related Art  
       [0004] In all fields of engine design, there is an increasing emphasis on obtaining more effective emission control, better fuel economy and, at the same time, continued high power output. This trend has resulted in the substitution of fuel injection systems for carburetors as the engine charge former. In the common systems used, fuel is injected into an intake air manifold. In order to obtain still further improvement, direct injection systems are being considered. These systems inject fuel directly into the combustion chamber and thus have significant potential advantages such as fine emission control.  
       [0005] An injection nozzle of a fuel injector employed in a conventional direct injection system is exposed to a combustion chamber through an opening formed in a cylinder head assembly. A forked member usually is used to affix the fuel injector onto the cylinder head assembly. The forked member is secured to the cylinder head assembly with a fastener such as a bolt. Meanwhile, the forked member contacts the body of the fuel injector with its forked section to push a flange of the fuel injector toward the combustion chamber so that the injection nozzle of the fuel injector can be exposed to the combustion chamber.  
       [0006] The fuel injector often has a mount section between the flange and the injection nozzle. This mount section has a diameter larger than a diameter of the injection nozzle but smaller than a diameter of the flange.  
       [0007] The cylinder head opening includes two sections: a small diameter opening section and a large diameter opening sections. A generally square step occurs at the transition between the two opening sections.  
       [0008] The mount section of the fuel injector is seated at this step portion and loaded by the forked member. A seal member, such as a disc spring, conventionally is provided between the mount section of the fuel injector and the step portion to seal up this area.  
       [0009] On occasion, the loading on the fuel injector and thus on the seal can be non-uniform around the seal and can be less than a desired loading. The effectiveness of the seal thus is jeopardized. This occurs because the configuration of the forked member and the surface of the cylinder head on which it is mounted vary due to manufacturing tolerances. If these tolerances stack-up adversely, the forked member does not squarely load the fuel injector, and thus the loading around the seal is not uniform. At the extreme, the fuel injector can assume a noticeably skewed orientation relative to a central axis of the opening in which is mounted.  
       [0010] Hot gases and flames can leak through the seal if the fork member does not properly load the fuel injector and compress the seal. That is, if the seal is not uniform and one section of the seal is not properly compressed, hot gases and flames will leak through the improperly loaded section of the seal. The injector nozzle consequently is excessively heated and deposits can form on the nozzle. These deposits can block and clog the nozzle apertures thereby preventing proper fuel injection and effecting engine performance and emission control.  
       SUMMARY OF THE INVENTION  
       [0011] A need therefore exists for a mounting construction of the fuel injector that consistently produces an effective seal between fuel injector and the engine body.  
       [0012] In accordance with one aspect of the present invention, a direct fuel injected, internal combustion engine comprises an engine body defining, at least in part, at least one combustion chamber. A fuel injector is arranged to spray fuel directly into the combustion chamber. The engine body has an opening through which the fuel injector is inserted, and the fuel injector having a contact surface. A thrust member is arranged to exert a loading onto the contact surface toward the combustion chamber, and a fixing member affixes the thrust member onto the engine body. A sealing member is disposed within a space between the fuel injector and the opening. The thrust member includes a thrust section contacting the contact surface of the fuel injector and a fixing section at which the thrust member is affixed onto the engine body by the fixing member. At least one of the thrust section and the fixing section having a convex surface.  
       [0013] The convex surface allows for varying orientations of the thrust member relative to the engine body when mounted to the engine body. The thrust member in this manner can squarely load the fuel injector contact surface such that the applied force is substantially uniform about the contact surface despite manufacturing tolerance stack-ups. The generally uniform pressure about the contact surface at a desired loading produces uniform pressure about the sealing member to produce an effective seal between the fuel injector and the engine body, thereby inhibiting overheating of the fuel injector and deposit formations on a fuel injector nozzle.  
       [0014] Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0015] These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention, and which;  
     [0016]FIG. 1 is a schematic view of an engine which is configured in accordance with the preferred embodiment of the present invention as employed on an outboard motor, and illustrates in Sections  1 A the outboard motor from a side elevational view, illustrates in Sections  1 B and  1 C a partial schematic view of the engine with associated portions of induction and fuel supply systems, illustrates in Section  1 D a sectional view of the engine (as taken along line I-I of the Section  1 B) and a portion of a driveshaft housing of the outboard motor, and illustrates an electronic control unit (ECU) of an engine control system communicating with various sensors and controlled components of the engine;  
     [0017]FIG. 2 is a top plan view showing a power head incorporating the engine with the engine shown in solid lines and a protective cowling shown in phantom;  
     [0018]FIG. 3 is a schematic perspective view showing components relating to a high pressure fuel injection assembly exploded from the engine, and is taken generally in the direction of the arrow  3  in FIG. 2;  
     [0019]FIG. 4 is an elevational view showing a main cylinder head member taken in the direction of the arrow  4  in FIG. 8, and particularly illustrates a water flow path in a cooling system employed in the engine;  
     [0020]FIG. 5 is an elevational and upper partial view showing the same main cylinder head member taken in the direction of the arrow  5  in FIG. 8 and illustrates particularly another section of the water flow path in the same cooling system;  
     [0021]FIG. 6 is a cross-sectional view showing the same main cylinder head member of FIG. 5 taken along the line  6 - 6  in FIG. 5;  
     [0022]FIG. 7 is a schematic view generally showing the entire water flow path in the cooling system;  
     [0023]FIG. 8 is a cross-sectional plan view showing a preferred embodiment of a mounting construction for a fuel injector onto a cylinder head assembly;  
     [0024]FIG. 9 is an enlarged partial elevational view showing the same mounting construction taken in the direction from the arrow  9  in FIG. 8;  
     [0025]FIG. 10 is an enlarged partial cross-sectional view showing the same mounting construction taken along the line  10 - 10  in FIG. 8;  
     [0026] FIGS.  11 (A) to (C) show a thrust member used for mounting the fuel injector; FIG. 11(A), (B),(C) are a top plan view, a lateral side view and a longitudinal side view, respectively;  
     [0027]FIG. 12 is an elevational side view of a bolt of the mounting construction;  
     [0028]FIG. 13 is a cross-sectional plan view showing another preferred embodiment of the mounting construction;  
     [0029]FIG. 14 is an enlarged partial elevational view showing the same mounting construction taken in the direction from the arrow  14  in FIG. 13;  
     [0030]FIG. 15 is an enlarged elevational view showing and additional embodiment of the mounting construction; and  
     [0031]FIG. 16 is a top plan view showing a power head which incorporates a four stroke engine that can be provided with the embodiment of the present invention, with the engine shown in solid lines and a protective cowling shown in phantom. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION  
     [0032] The general overall environment in which the invention is practiced and certain details of the engine will be described primarily with reference to FIG. 1.  
     [0033] In FIG. 1A, an outboard motor constructed and operated in accordance with an embodiment of the invention is depicted in side elevational view and is identified generally by the reference numeral  30 .  
     [0034] The entire outboard motor  30  is not depicted in that the swivel bracket and clamping bracket that are associated with the driveshaft housing, indicated generally by the reference numeral  32 , are not illustrated. This is because these components are well known in the art and the specific method by which the outboard motor  30  is mounted to the transom of an associated watercraft is not necessary to permit those skilled in the art to understand or practice the invention.  
     [0035] The outboard motor  30  includes a power head, indicated generally by the reference numeral  34 , that is positioned above the driveshaft housing  32  and which includes a powering internal combustion engine, indicated generally by the reference numeral  36 . This engine  36  is shown in more detail in the remaining two views of this figure and will be described shortly by reference thereto.  
     [0036] The power head  34  is completed by a protective cowling which includes a top cowling member  38  and a bottom cowling  40 . This top cowling member  38  is detachably connected to the bottom cowling member  40  which is a lower tray portion of the protective cowling and encircles an upper portion of the driveshaft housing  32 , particularly an exhaust guide  42  for an exhaust system of the engine  36 .  
     [0037] The top cowling member  38  has a pair of compartments (not shown) placed at rear and both sides of its body. The compartments open rearward so that air is introduced into these compartments. Air inlet barrels  44  (see FIG. 2), which have no bottom portion, stand in the respective compartments. The air inlet barrels  44  look like a funnel and the compartments are connected with interior of the top cowling member  38  through the air inlet barrel  44 . Thus, the air is admitted into interior of the top cowling member  38  and then goes to an air induction system, indicated generally by the reference numeral  46 .  
     [0038] Positioned beneath the driveshaft housing  32  is a lower unit  48  in which a propeller  50 , which forms the propulsion device for the associated watercraft, is journaled.  
     [0039] As is typical with outboard motor practice, the engine  36  is supported in the power head  34  so that its crankshaft or output shaft  54  (see the upper view) rotates about a vertically extending axis. This is done so as to facilitate connection of the crankshaft  54  to a driveshaft (not shown) which depends into the driveshaft housing  32  and which drives the propeller  50  through a conventional forward, neutral, reverse transmission contained in the lower unit  48 .  
     [0040] The details of the construction of the outboard motor  30  and the components which are not illustrated may be considered to be conventional or of any type known to those wishing to utilize the invention disclosed herein. Those skilled in the art can readily refer to any known constructions with which to practice the invention.  
     [0041] With reference now in detail to the construction of the engine  36  still by primary reference to FIG. 1, in the illustrated embodiment, the engine  36  is of the V6 type and operates on a two stroke, crankcase compression principle. Although the invention is described in conjunction with an engine having this cylinder number and cylinder configuration, it will be readily apparent that the invention can be utilized with engines having other cylinder numbers and other cylinder configurations.  
     [0042] Also, although the engine  36  will be described as operating on a two stroke principle, it will also be apparent to those skilled in the art that almost all facets of the invention can be employed in conjunction with four stroke engines as noted later.  
     [0043] The engine  36  comprises a cylinder block  56  that is formed with a pair of cylinder banks  58 . Each of these cylinder banks  58  is formed with three vertically spaced, horizontally extending cylinder bores  60 . Pistons  62  reciprocate in these cylinder bores  60 .  
     [0044] The pistons  62  are, in turn, connected to the upper or small ends of connecting rods  64 . The big ends of these connecting rods  64  are journaled on the throws of the crankshaft  54  in a manner that is well known in this art.  
     [0045] The crankshaft  54  is journaled in a suitable manner for rotation within a crankcase chamber  68  that is formed in part by a crankcase member  70  that is affixed to the cylinder block  56  in a suitable manner. The cylinder block  56  and the crankcase member  70  generally define an engine body. As is typical with two stroke engines, the crankshaft  54  and crankcase chamber  68  are formed with seals so that each section of the crankcase that is associated with one of the cylinder bores  60  will be sealed from the others. This type of construction is well known in the art.  
     [0046] A cylinder head assembly, indicated generally by the reference numeral  72 , is affixed to the end of the cylinder banks  58  that are spaced from the crankcase chamber  68 . These cylinder head assemblies  72  are comprised of a main cylinder head member  74  that defines a plurality of recesses  76  (see FIG. 8) in its lower face. Each of these recesses  76  corporate with the respective cylinder bore  60  and the head of the piston  62  to define the combustion chambers  78  of the engine  36 . This is also well known in the art. A cylinder head cover member  80  completes the cylinder head assembly  72 . The main cylinder head members  74  and the cylinder block  56  are affixed to each other and to the respective cylinder banks  58  in a suitable, known manner.  
     [0047] The air induction system  46  is provided for delivering an air charge to the sections of the crankcase chamber  68  associated with each of the cylinder bores  60 . This communication is via an intake port  82  formed in the crankcase member  70  and registering with each such crankcase chamber section.  
     [0048] The induction system  46  includes an air silencing and inlet device, shown schematically in this figure and indicated by the reference numeral  84 . The actual construction of this air charge device appears in FIGS. 2. In actual physical location, this device  84  is contained within the top cowling member  38  at the forward end thereof and has a rearward facing air inlet opening  86  through which air is introduced.  
     [0049] The air inlet device  84  supplies the induced air to a plurality of throttle bodies  88 , each of which has a throttle valve  90  provided therein. These throttle valves  90  are supported on throttle valve shafts (not shown). These throttle valve shafts are linked to each other for simultaneous opening and closing of the throttle valves  90  in a manner that is well known in this art.  
     [0050] As is also typical in two stroke engine practice, the intake ports  82  have, provided in them, reed-type check valves  92 . These check valves  92  permit the air to flow into the sections of the crankcase chamber  68  when the pistons  62  are moving upwardly in their respective cylinder bores. However, as the pistons  62  move downwardly, the charge will be compressed in the sections of the crankcase chamber  68 . At that time, the reed type check valve  92  will close so as to permit the charge to be compressed. In addition, lubricant pumps  94  are provided for spraying lubricant into the throttle bodies  88  for engine lubrication under the control of an ECU (Electronic Control Unit)  96  that will be described more in detail later. Although it is not shown, some forms of direct lubrication may be also employed for delivering lubricant directly to certain components of the engine.  
     [0051] The charge which is compressed in the sections of the crankcase chamber  68  is then transferred to the combustion chambers  78  as through a scavenging system (not shown) in a manner that is well known. As best seen in FIG. 8, spark plug  98  is inserted into an opening  100  formed at a boss  101  for each combustion chamber  78 . The spark plug  98 , in turn, fire a fuel air charge that is formed by mixing fuel directly with the intake air via a fuel injector  102  in each combustion chamber  78 . The fuel injectors  102  are solenoid type and electrically operated also under the control of the ECU  96 . The fuel injectors  102  are mounted directly in the cylinder head member  74  in a specific location, as will be described, so as to provide optimum fuel vaporization under all running conditions.  
     [0052] As seen in Figure Sections  1 B and  1 C, fuel is supplied to the fuel injectors  102  by a fuel supply system, indicated generally by the reference numeral  104 . The fuel supply system  104  comprises a main fuel supply tank  108  that is provided in the hull of the watercraft with which the outboard motor  30  is associated. Fuel is drawn from this tank  108  through a conduit  110  by means of a first low pressure pump  112  and a plurality of second low pressure pumps  114 . The first low pressure pump  112  is a manually operated pump and the second low pressure pumps  114  are diaphragm type pumps operated by variations in pressure in the sections of the crankcase chamber  68 , and thus provide a relatively low pressure. A quick disconnect coupling (not shown) is provided in the conduit  110  and also a fuel filter  116  is positioned in the conduit  110  at an appropriate location.  
     [0053] From the low pressure pump  114 , fuel is supplied to a vapor separator  118  which is mounted on the engine  36  or within the top cowling member  38  at an appropriate location. This fuel is supplied through a line  120 . At the vapor separator end of the line  120 , there is provided at a float valve (not shown) that is operated by a float  122  so as to maintain a uniform level of fuel in the vapor separator  118 .  
     [0054] A high pressure electric fuel pump  124  is provided in the vapor separator  118  and pressurizes fuel that is delivered through a fuel supply line  126  to a high pressure pumping apparatus, indicated generally by the reference numeral  128 . The electric fuel pump  124 , which is driven by an electric motor, develops a pressure such as 3 to 10 kg/cm 2 . A low pressure regulator  130  is positioned in the fuel supply line  126  at the vapor separator  118  and limits the pressure that is delivered to the high pressure pumping apparatus  128  by dumping the fuel back to the vapor separator  118 .  
     [0055] The high pressure fuel pump  128  that can develop a pressure of, for example, 50 to 100 kg/cm 2  or more. A pump drive unit  132  (the lower left hand view) is provided for driving the high pressure fuel pump  128 .  
     [0056] With reference primarily to FIGS. 2 and 3, the high pressure fuel pump  128  is mounted on the pump drive unit  132  with bolts  134 . A stay  138  is affixed to the cylinder block  56  at a boss  140  with a bolt  142  and at a boss  144  with a bolt  146 . Then, the pump drive unit  132  is affixed to the stay  138  at a bolt hole  148  with a bolt  150  and at bolt hole  152  with a bolt  154 . The pump drive unit  132  is, further, affixed to the cylinder block  56  directly at a boss  156  with a bolt  158 . Thus, the pump drive unit  132  overhangs between the two banks  58  of the V arrangement. A pulley  160  is affixed to a pump drive shaft  162  of the pump drive unit  132 . The pulley  160  is driven by a drive pulley  164  affixed to the crankshaft  54  by means of a drive belt  166 . The pump drive shaft  162  is provided with a cam disc  168  existing horizontally for pushing plungers (not shown) which are disposed on the high pressure fuel pump  128 .  
     [0057] The high pressure fuel pump  128  has a unified fuel inlet and outlet module  170  which is mounted on a side wall of the pressure pump  128 . The inlet and outlet module  170  has an inlet passage (not shown) connected to the fuel supply line  126  with a connector  172 , while an outlet passage (not shown) is connected to a pair of flexible conduits  174  with a connector  176 .  
     [0058] As seen in FIG. 1C, the pressure of the fuel supplied by the fuel pump  128  is regulated to be the fixed value by a high pressure regulator  180  which dumps fuel back to the vapor separator  118  through a pressure relief line  182  in which a fuel heat exchanger or cooler  184  is provided. It is important to keep the fuel under the constant pressure. Because the fuel amounts are determined by changes of duration of injection under the condition that the pressure for injection is always the same.  
     [0059] As seen in FIGS. 2 and 3, the flexible conduits  174  are connected to fuel supply rails  186  with connectors  185 . The fuel supply rails  186  are made of metal so as to be rigid. The fuel supply rails  186  communicate with the flexible conduits  174  and also fuel injectors  102  when they are held on the fuel supply rails  186 .  
     [0060] The respective fuel rails  186  are affixed to both of the main cylinder head members  74  at bosses  188  with positioning bolts  190 . Apertures  191  are provided on the fuel rails  186  for the positioning bolts  190  passing through the apertures  191 . The fuel injectors  102  are held between the fuel supply rails  186  and the cylinder head members  74 . Mount sections  192  of the fuel injectors  102  are inserted into bosses  194  so as to be exposed to combustion chambers. Flange portions  196  of the fuel injectors  102  are supported with forked members  198  that are affixed to the cylinder head member  74  at bosses  200  with bolts  202 . The flange portion  196  on each fuel injector  102  extends about the fuel injector  102 , generally surrounding the injector nozzle (although the nozzle is spaced from flange portion along a longitudinal axis of the injector body). In the illustrated embodiment, the flange portion generally encircles the injector nozzle. The bosses  200  can be replaced by other positioning constructions. An additional construction is shown in FIG. 8 and will be described later.  
     [0061] The forked member  198  is made of anti-corrosive metal such as stainless steel and aluminum or synthetic resin. In this manner, the forked member  198  is prevented from corroding and deteriorating, and maintains its shape and integrity in order to apply a generally constant loading on the fuel injector. The fuel injector mounting construction and loading will be described in more detail below.  
     [0062] Although the same bosses  188 ,  194 ,  200  are provided on the cylinder head member  74  of the other bank  58 , they are simply schematically shown in FIG. 3 for avoiding redundancy. The high pressure fuel pump  128 , pump drive unit  132 , inlet and outlet module  170 , flexible conduits  174 , fuel rails  186  and fuel injectors  102  are unified together. These unified components form a high pressure fuel injection assembly  206 . The affixing construction including the mounting structure of the fuel injector  102  will be described more in detail with reference to FIGS. 8, 9 and  10  later.  
     [0063] Fuel is supplied from the high pressure fuel pump  128  to the flexible fuel conduits  174 . The fuel conduits  174 , in turn, deliver fuel to a pair of vertically extending fuel rails  186 . The fuel rails  186 , then, supply fuel to the fuel injectors  102 .  
     [0064] As seen in FIG. 1B, after the fuel charge has been formed in the combustion chambers by the injection of fuel from the fuel injectors  102 , the charge is fired by firing the spark plugs  98 . The injection timing and duration, as well as the control for the timing of firing of the spark plugs  98 , are controlled by the ECU  96 .  
     [0065] Once the charge burns and expands, the pistons  62  will be driven downwardly in the cylinder bores  60  until the pistons  62  reach the lowermost position. At this time, an exhaust port (not shown) will be uncovered so as to open the communication with an exhaust passage  204  formed in the cylinder block  56 . The exhaust gasses flow through the exhaust passages  204  to manifold collector sections  206  of respective exhaust manifolds that are formed within the cylinder block  56 . These exhaust manifold collector sections  206  communicate with exhaust passages formed in an exhaust guide plate  42  on which the engine  36  is mounted.  
     [0066] A pair of exhaust pipes  208  depend from the exhaust guide plate  42  and extends the exhaust passages  204  into an expansion chamber  210  formed in the driveshaft housing  32 . From this expansion chamber  210 , the exhaust gasses are discharged to the atmosphere through a suitable exhaust system. As is well known in outboard motor practice, this may include an underwater, high speed exhaust gas discharge and an above the water, low speed exhaust gas discharge. Since these types of systems are well known in the art, a further description of them is not believed to be necessary to permit those skilled in the art to practice the invention.  
     [0067] A feedback control system, indicated generally by the reference numeral  214  is provided for realizing a control strategy along which the initiation and duration of fuel injection from the fuel injector  102  and timing of firing of the spark plugs  98  are controlled. The feedback control system  214  comprises the ECU  96  and a number of sensors which sense either engine running conditions, ambient conditions or conditions of the outboard motor  30  that will effect engine performance. Certain of the sensors are shown schematically in FIG. 1 and will be described by reference to that figure.  
     [0068] There is provided, associated with the crankshaft  54 , a crankshaft angle position sensor  216  which, when measuring crankshaft angle versus time, outputs a crankshaft rotational speed signal or engine speed signal indicated schematically at  218  to the ECU  96 .  
     [0069] Operator demand or engine load, as determined by throttle angle of the throttle valve  90 , is sensed by a throttle position sensor  220  which outputs a throttle position or load signal  222  to the ECU  96 . When the operator desires to gather speed, i.e., accelerate the engine speed, a throttle on a steering handle (not shown) is operated by the operator. The throttle valve  90  is, then, going to open toward the certain open position that corresponds to the desired speed at which air charge is induced more than before into the crankcase chamber  68  through the throttle bodies  88 . Also, the engine load increases, for example, when the associated watercraft advances against wind. In this situation, the operator also operates the throttle so as to recover the speed that may be lost.  
     [0070] A combustion condition or oxygen ( 02 ) sensor  224  is provided that senses the in cylinder combustion conditions by sensing the residual amount of oxygen in the combustion products at a time near the time when the exhaust port is opened. This output and air fuel ratio signal is indicted schematically at  226  to the ECU  96 .  
     [0071] There is also provided a pressure sensor  228  in line connected to the pressure regulator  180 . This pressure sensor  228  outputs the high pressure fuel signal to the ECU  96 , which signal line is omitted in FIG. 1.  
     [0072] There also may be provided a water temperature sensor  230  (see the lower right-hand view) which outputs a cooling water temperature signal  232  to the ECU  96 .  
     [0073] Further, an intake air temperature sensor  234  (see the upper view) is provided and this sensor  234  outputs an intake air temperature signal  236  to the ECU  96 .  
     [0074] Although these are all sensors shown in FIG. 1, it is, of course, practicable to provide other sensors such as an engine height sensor, a trim angle sensor, a knock sensor, a neutral sensor, a watercraft pitch sensor and an atmospheric temperature sensor in accordance with various control strategies.  
     [0075] The ECU  96 , as has been noted, outputs signals to the fuel injectors  102 , spark plugs  75 , the lubrication pumps  94  and the high pressure electric fuel pump  124  for their respective control. These control signals are indicated schematically in FIG. 1 at  238 ,  240 ,  242  and  244 , respectively.  
     [0076] In addition (see FIG. 2), a starter motor  246  for starting the engine  36 , a tensioner  248  for giving tension to the belt  166 , a flywheel  250  and a cover member  252  for covering the rotating components such as the high pressure fuel pump  128  are provided.  
     [0077] The outboard motor  30  has an engine cooling system. With reference to FIGS. 4 through 8, primarily the cooling system will now be described below. The mounting structure of the fuel injector  102  will be partly included in the following descriptions.  
     [0078] The engine cooling system is generally indicated with the reference numeral  254 . Actually, the main cylinder head member  74  of the cylinder head assembly  72  is affixed to the cylinder block  56  via a gasket  256  (see FIG. 7). The main cylinder head member  74  has the aforenoted boss  194  for holding the mount section  192  of the fuel injector  102  (see FIG. 8). The axis of the boss  194  has a certain angle relative to the cylinder bore axis  258  so that the fuel injector  102  is placed slantwise relative to the axis  258 . Injection nozzles  260  of the fuel injectors  102  are exposed to the combustion chambers  78  through openings  262  formed at the bottom of the recess in the bosses  194 . The injection nozzles  260  have a single or a plurality of injection apertures. The fuel injector  102  and the spark plug  98  are adjoined each other.  
     [0079] A gasket  264  is provided between the main cylinder head member  74  and the cylinder head cover member  80 . The cylinder head cover member  80 , main cylinder head member  74  and cylinder block  56  are securely connected with connecting bolts (not shown) in a known manner.  
     [0080] As schematically shown in FIG. 7, a cooling jacket  266  is formed circumferentially around the cylinder bore  60 . Another cooling jacket or cylinder head upstream jacket  268  is also formed circumferentially around the recess  76  of the main cylinder head member  74 . Also, generally around the bosses  101  for the spark plug  98  and at periphery of the bosses  194  for the fuel injector  102  in the cylinder head member  74 , still another cooling jacket or cylinder head downstream jacket  270  is formed. Further, the cylinder head cover member  80  also has a cooling jacket  271  (see FIG. 7). This cooling jacket  271  does not appear in FIG. 8.  
     [0081] The gasket  256  has upper communication apertures  272  at its almost uppermost portion (see FIGS. 4 and 7) so as to allow water flowing into the cylinder head upstream jacket  268  from the cylinder block cooling jacket  266 . Cavities  276  are located in the upstream jacket  268  (see FIGS. 6 and 8) and in the close proximity to the bosses  194  for the mount sections  192  of the fuel injectors  102 . That is, the cavities  276  are formed deeper than the other part of the cylinder head upstream jacket  268 . Because of this, cooling water is permitted to approach closer to the mount sections  192  of the fuel injectors  102 .  
     [0082] Lower communication apertures  278  are provided at the almost lowermost portion of the main cylinder head member  74  to discharge the water from the cylinder head upstream jacket  268  and then supply it to the downstream jacket  270 . Middle communication apertures  280  are provided between the upper cylinder UC and the middle cylinder MC and also between the middle cylinder MC and the lower cylinder LC for allowing water, again, to flow from the upstream jacket  268  to the downstream jacket  270 .  
     [0083] Bypasses  282  are provided at the respective cylinders UC, MC and LC for further cooling the respective fuel injectors  102 . As best seen in FIGS. 5 and 6, the bypasses  282  are placed directly under the fuel injector bosses  194  and allow water to flow from the downstream jacket  270  to the other water passage  229 . The water flowing through these bypasses  282  can take heat away from the main cylinder head member  74  around the bypasses  282 , which includes the fuel injector bosses  194 .  
     [0084] The water flow in this cooling system  254  will be again described more in detail with reference to FIG. 7. Water is introduced into the cooling system  254  from the body of water surrounding the outboard motor  30  by means of a water pump  290 . Some amounts of this water is used for cooling the exhaust system and the reminder of the water is supplied to the cylinder block cooling jacket  266  for cooling the cylinder block  56  (the respective cylinders UC, MC and LC). Next, the water goes into the cylinder head upstream jacket  268  through the upper communication apertures  272 . Primarily, the water is then flow into the downstream jacket  270  through the lower communication apertures  278 . However, additionally, some of the water goes into the downstream jacket  270  en route through middle communication apertures  280 . The water flow in the cylinder head upstream jacket  268  and the downstream jacket  270  cools the body of the main cylinder head member  74 .  
     [0085] Further, in this embodiment, the water in the upstream jacket  268  goes into the downstream jacket  270  through the bypasses  282  During flowing through these bypasses  282 , the water expedites the cooling effect of the fuel injector bosses  194  and eventually the cooling effect of the fuel injectors  102 .  
     [0086] The water, then, goes to a thermostat compartment  292  wherein a conventional thermostat is placed. After passing through the thermostat compartment  292 , the water goes to the water jacket  271  in the cylinder head cover member  80  for cooling this portion and finally is discharged to the body of water outside of the outboard motor  30 .  
     [0087] As described above, because the cylinder head upstream jacket  268 , downstream jacket  270 , cavities  276  and bypass passages  282  are provided in this cooling system  254 , the fuel injectors  102  and spark plugs  98  are effectively cooled down as well as the cylinder head assembly  72 . In addition, the bolt  202  is positioned at an generally opposite place of the spark plug  98  relative to the fuel injector  102 . Accordingly, the bolt  202  will not prevent cooling water from flowing smoothly in such an limited narrow space.  
     [0088] The mounting construction of the fuel injectors  102  will now be described in detail with reference to FIGS. 8 through 12. Although a plurality of fuel injectors  102  are mounted for multiple cylinders of the engine  36  in this embodiment, one fuel injector  102  will represent the other injectors because the same structure can be applied for them.  
     [0089] As described above, the forked member  198  is used for securing the fuel injector  102  onto the main cylinder head member  74  and further for exerting a loading or thrust force upon the fuel injector  102  toward the combustion chamber  78 . Thus, the forked member functions as a thrust member. As best seen in FIGS.  11 (A) to (C), the forked member  198  generally has two sections: a fixing section  294  and a forked or thrust section  295 . The forked section  295  is formed with thrust portions  296  and an intermediate portion  298 . In the illustrated embodiment, the fixing section  294  has convex surfaces  299 , which curvature is R1, on both sides. The thrust portions  296  also have convex surfaces  300 , which curvature is R2, at least on the side contacting the flange  196 . The intermediate portion  298  has concave surfaces unlike the fixing section  294  and the thrust portion  296 . As understood from FIGS. 11B and 11C, the fixing portion  294  is curved in a lateral direction, while the thrust portions  296  are curved in a longitudinal direction. This allows the forked member  198  to roll and pitch relative to the fuel injector flange  196  and the mounting surface of the cylinder head member  74  when assembled, as noted below.  
     [0090] The fixing section  294  has a bolt hole  301  which allows the fixing section  294  to pivot or yaw for position adjustment relative to the fuel injector  102 , as described below. The bolt  202  is a special bolt as shown in FIG. 12 and used for affixing the forked member  198  to the cylinder head member  74  as a fixing member. That is, the bolt  202  has a protrusion  306  which has a generally partial spherical surface at its periphery and under its head portion  308 . The fixing section  294  has, therefore, a generally partial spherical recess  310  around the bolt hole  300  to receive the spherical protrusion  306 .  
     [0091] The main cylinder head member  74  has a relatively shallow hollow portion  312 . Because the fixing section  294  is projected from the intermediate portion  298 , the forked member  198  can be positioned at the hollow  312  and registered with a projected surface  299 . That is, the forked member  198  can be temporarily placed and aligned on the cylinder head member  74  before it is fixed to the cylinder head member  74  for the accurate positioning.  
     [0092] The mount section  192  of the fuel injector  102  is formed between the flange  196  and the injection nozzle  260 . This mount section  192  has a diameter larger than a diameter of the injection nozzle  260  but smaller than a diameter of the flange  196 . An opening  316 , of a diameter larger than a diameter of the nozzle opening  262 , is formed at the boss  194  in the cylinder head member  74  so that these openings  262 ,  316  are sections of a single opening. A step portion  318  occurs at the transition between the large opening  316  and the small opening  262 . The mount section  192  of the fuel injector  102  is seated at this step portion  318 . A disc spring  320  is provided between the mount section  192  and the step portion  318  to seal up this area.  
     [0093] The flange  196  has a surface  321  at which the thrust portions  296  of the forked member  198  contact. The surface  321  is generally flat.  
     [0094] The forked member  198  is affixed to the cylinder head member  74  with the bolt  202 . The forked section  295  receives the fuel injector  102  between the thrust portions  296 . When the bolt  202  is fastened tight, the thrust portions  296  apply a force on the fuel injector flange  196  in a direction toward the combustion chamber  78 . That is, the forked member  198  acts as a leaf spring and loads the fuel injection in a direction toward the step  318 . In particular, the forked member  198  directly exerts the thrust force or loading onto the contact surface  321  of the flange  196  with the thrust portions  296 . This loading is also exerted upon the disc spring  320  so that the spring  320  is compressed and seals the area between the cylinder head member  74  and the fuel injector  102 .  
     [0095] The forked member  198  applies a generally uniform loading about the flange  196 , and thus on the disc spring  320  despite manufacturing tolerances. In accordance with the embodiment of the present invention, the forked member  198  has the fixing section  294  and the forked section  295 , both of which have the convex surfaces  299 ,  300  with curvatures of R1 and R2, respectively. These convex surfaces  299 ,  300  allow the forked member  198  to incline itself That is, the forked member  198  has a self adjustment function in positioning that allows the forked member  198  to assume a variety of orientations relative to the cylinder head member  74  so as to accommodate for manufacturing tolerances while still squarely loading the fuel injection  102  relative to the step  318  (i.e., the applied force is generally normal to the step  318 ). Accordingly, any distorted or non-uniform loading on the disc spring  320  can be avoided and hence the sealing effect by the disc spring  320  can be uniform. As a result, gasses leak and carbon deposits on the injection nozzle  260  are inhibited.  
     [0096] The self-orienting feature can also be accomplishes by forming the convex surface of the cylinder head member  74  with a curved surface that acts a fulcrum over which the fixing section  294  can pitch, roll and/or yaw in order to allow the fuel injector flange  196  to sit squarely against the step  318  within the opening. In this variation, the curved protrusion lies on the surface of the cylinder head within the hollow  312  with the mounting hole for the bolt  202  being positioned generally at the center of the curved protrusion. The curved protrusion preferably has a radius of curvature R1. This construction thus can be used with a forked member  198  having a flat fixing section  294  and convex thrust portions  296 .  
     [0097] Preferably both mounting constructions would also include the combination of the spherical bolt protrusion  306  and the spherical recess in the forked member  198 . This allows the forked member  198  to be fixed to the cylinder head member  74  without imparting a significant force in an oblique or parallel direction relative to the step  318 .  
     [0098] In addition, the combination of the spherical protrusion  306  of the bolt  202  with the spherical recess  310  also inhibits unintentional loosing of the bolt  202 . This is particularly useful for the forked member  198 . That is, due to the curved configuration of the forked member  198 , the bolt  202  can loosen. However, because of the combination of the spherical protrusion  306  and the spherical recess  310 , the looseness of the bolt  202  can be inhibited. It should be noted that the protrusion  306  having the partial spherical surface and the same configured recess  310  of the forked member  198  is dispensable if the bolt  202  would not loosen, for instance, if other types of locking mechanisms are used (e.g., a lock washer).  
     [0099] The fuel injector  102  has its own axis, while the bolt  202  has also its own axis. After being affixed, both of the axes extend parallel relative to each other. Also, the contact surface  321  of the flange  196  and chord lengths across the ends of the convex surfaces  299  of the forked member  198  extend generally normal to the axes.  
     [0100] With reference to FIGS. 13 and 14, another arrangement for temporarily supporting the forked member  198  will be described. The same members already described by reference to FIGS. 1 through 12 will be assigned with the same reference numerals and not described again for avoiding redundancy. Additionally, these same members will also be ascribed the same reference numerals in connection with the description of the embodiments illustrated in FIGS. 15 and 16. The above description of these members, which are common among the embodiments, therefore applies equally to all embodiments unless indicated otherwise.  
     [0101] In this arrangement, pins  330  are connected to the cylinder head member  74  and act as projections at respective positions on the main cylinder head member  74 . The pins  330  can temporarily support the forked members  198  instead of the hollows  312  shown in FIG. 8.  
     [0102] With reference to FIG. 15, still another arrangement for temporarily supporting the forked member  198  will be described. In this arrangement, the forked members  198  are unified with each other. That is, the respective forked members  198  are joined with the connecting sections  332 .  
     [0103] The features of the present invention can be embodied in an engine other than the two stroke, crankcase compression engine as described above. For instance, a four stroke engine such as an engine  336  shown in FIG. 16 can employ the features. In this engine  336 , a pump drive unit  338  is provided on the engine  336  and a pair of high pressure fuel pumps  340  are located at both sides of the pump drive unit  338 . A pair of fuel supply rails  342  are provided and connected with the high pressure fuel pumps  340  with flexible conduits  344 . Special components for the four stroke engine  336  are, for example, an intake valve  346  and a camshaft  348 .  
     [0104] The features and aspects of the present invention are applicable not only to outboard motors but also to other engines for marine propulsion systems such as stem drive systems, for land vehicles such as motorcycles and automobiles, and for utility machines such as lawn mowers. Stationary engines can also employ them.  
     [0105] Although this invention has been described in terms of a certain preferred embodiment, other embodiments apparent to those of ordinary skill in the art are also within the scope of this invention. Accordingly, the scope of the invention is intended to be defined only by the claims that follow.