Patent Publication Number: US-2009229574-A1

Title: Fuel injection device, an engine including the same, and vehicle

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fuel injection device, an engine including the same, and a vehicle. 
     2. Description of the Related Art 
     In a vehicle such as a motorcycle, a fuel injection engine including a fuel injection device (injector) as a fuel supply is mounted instead of a conventional carburetor. Using this fuel injection device improves efficiency of fuel control, providing purification of exhaust gas, low-fuel consumption or other advantages. 
     Among such fuel injection devices as the fuel supply is a fuel injection device constituted by a nozzle in communication with a combustion chamber, an air-fuel injection valve attached to a cylinder head and a fuel injection valve that is connected to this air-fuel injection valve while injecting fuel into the air-fuel injection valve (see JP 2004-060610 A, for example). 
     In this fuel injection device, since an injector housing is integrally formed with a head cover, it is not necessary to arrange a member that constitutes the injector housing in the periphery of the cylinder head, thus achieving reduction in the number of components. 
     In the air-fuel injection engine described in JP 2004-060610 A, however, the air-fuel injection valve is sandwiched between the cylinder head and the head cover. Therefore, the fuel injection valve is required to be assembled into the head cover after the air-fuel injection valve is attached so as to be sandwiched between the cylinder head and the head cover. This causes poor workability of assembling the fuel injection valve and the air-fuel injection valve. 
     In addition, it is difficult to accurately position the air-fuel injection valve sandwiched between the cylinder head and the head cover with respect to the fuel injection valve attached to the cylinder head. 
     Moreover, the configuration of a space between the cylinder head and the head cover is not sufficiently simplified while rigidity of the fuel injection device composed of the fuel injection valve and the air-fuel injection valve is not improved. 
     SUMMARY OF THE INVENTION 
     In order to overcome the problems described above, preferred embodiments of the present invention provide a fuel injection device having greatly improved positioning accuracy, assembly performance and rigidity. 
     In addition, preferred embodiments of the present invention provide an engine having a greatly simplified configuration and a vehicle including the same. 
     According to a preferred embodiment of the present invention, a fuel injection device that injects a mixture of fuel and air includes a fuel injector that injects fuel, an air-fuel mixture chamber that produces the air-fuel mixture by mixing the fuel injected by the fuel injector and air, an air-fuel mixture injector that injects the air-fuel mixture produced by the air-fuel mixture chamber, and a holding member that holds the fuel injector and the air-fuel mixture injector. 
     In the fuel injection device, the fuel is injected by the fuel injector, and the injected fuel and air are mixed by the air-fuel mixture chamber, thereby producing the air-fuel mixture. The air-fuel mixture produced by the air-fuel mixture chamber is injected by the air-fuel mixture injector. The fuel injector and the air-fuel mixture injector are held by the holding member. 
     As described above, the fuel injector and the air-fuel mixture injector are integrated by the holding member, thereby eliminating the necessity of positioning the fuel injector and the air-fuel mixture injector. In addition, when the fuel injection device is attached to the engine, the fuel injector and the air-fuel mixture injector can be integrally handled. Furthermore, since the fuel injection device is provided separately from the engine, the fuel injection device can be attached to the assembled engine. Accordingly, workability of assembling the fuel injector and the air-fuel mixture injector is improved. 
     Moreover, a positional relationship between the fuel injector and the air-fuel mixture injector is fixed by the holding member, so that the positional relationship between the fuel injector and the air-fuel mixture injector is not affected by positions of other members of the engine. This improves positional accuracy of the fuel injector and the air-fuel mixture injector. 
     In addition, the fuel injector and the air-fuel mixture injector are integrally held by the holding member, so that rigidity of the fuel injection device is improved while its performance for sealing the air-fuel mixture is improved. 
     Furthermore, the fuel injector and the air-fuel mixture injector are integrally held by the holding member, so that the configuration of the engine is simplified and made compact. 
     The fuel injector and the air-fuel mixture injector may be coaxially arranged relative to each other. In this case, miniaturization is achieved while the air-fuel mixture is efficiently injected. 
     The air-fuel mixture chamber may be provided downstream of the fuel injector, and the air-fuel mixture injector may be provided downstream of the air-fuel mixture chamber. 
     In this case, the air-fuel mixture chamber is provided between the fuel injector and the air-fuel mixture injector, so that the fuel injector, the air-fuel mixture chamber and the air-fuel mixture injector are aligned. Accordingly, the configuration of the engine can be simplified and miniaturized. 
     The holding member may include an air supply passage through which air is supplied to the air-fuel mixture chamber. In this case, it is not necessary to additionally arrange the air supply passage within the engine. Thus, the internal configuration of the engine is simplified while workability of assembly is improved. Furthermore, the sealing performance of the air supply passage and the air-fuel mixture chamber is improved. 
     The air supply passage of the holding member may be arranged so as to extend from the air-fuel mixture chamber and along a side surface of the fuel injector. In this case, the engine can be further miniaturized and made compact. 
     The fuel injector may include a fuel injection valve at a tip, on a side of the air-fuel mixture chamber, of the fuel injector, and include a supply port for the fuel at a rear end of the fuel injector. 
     In this case, the fuel can be easily supplied to the supply port at the rear end of the fuel injector from the outside of the head cover of the engine. This prevents the internal configuration of the engine from being complicated. 
     The air-fuel mixture chamber may be provided in a space surrounded by the tip of the fuel injector, the air-fuel mixture injector and the holding member. 
     In this case, the configuration is further simplified, miniaturized and made compact. 
     According to another preferred embodiment of the present invention, an engine includes a fuel injection device, and the fuel injection device includes a fuel injector that injects fuel, an air-fuel mixture chamber that produces an air-fuel mixture by mixing the fuel injected by the fuel injector and air, an air-fuel mixture injector that injects the air-fuel mixture produced by the air-fuel mixture chamber, and a holding member that holds the fuel injector and the air-fuel mixture injector. 
     In the above-described fuel injection device, the fuel is injected by the fuel injector, and the injected fuel and air are mixed by the air-fuel mixture chamber, thereby producing the air-fuel mixture. The air-fuel mixture produced by the air-fuel mixture chamber is injected by the air-fuel mixture injector. The fuel injector and the air-fuel mixture injector are held by the holding member. 
     As described above, the fuel injector and the air-fuel mixture injector are integrated by the holding member, thereby eliminating the necessity of positioning the fuel injector and the air-fuel mixture injector. In addition, when the fuel injection device is attached to the engine, the fuel injector and the air-fuel mixture injector can be integrally handled. Furthermore, since the fuel injection device is provided separately from the engine, the fuel injection device can be attached to the assembled engine. Accordingly, workability of assembling the fuel injector and the air-fuel mixture injector is improved. 
     Moreover, a positional relationship between the fuel injector and the air-fuel mixture injector is fixed by the holding member, so that the positional relationship between the fuel injector and the air-fuel mixture injector is not affected by positions of other members of the engine. This improves the positional accuracy of the fuel injector and the air-fuel mixture injector. 
     In addition, the fuel injector and the air-fuel mixture injector preferably are integrally held by the holding member, so that rigidity of the fuel injection device is improved while its performance for sealing the air-fuel mixture is improved. 
     Furthermore, the fuel injector and the air-fuel mixture injector are integrally held by the holding member, so that the configuration of the engine is simplified and made compact. 
     Since such a fuel injection device is used, the configuration of the engine is simplified while workability of assembling the engine becomes easy. In addition, positioning accuracy of the fuel injection device of the engine is improved. Thus, reduction in weight and cost and higher performance of the engine can be achieved. 
     According to yet another preferred embodiment of the present invention, a vehicle includes an engine and a drive wheel driven by power generated by the engine, the engine includes a fuel injection device, and the fuel injection device includes a fuel injector that injects fuel, an air-fuel mixture chamber that produces an air-fuel mixture by mixing the fuel injected by the fuel injector and air, an air-fuel mixture injector that injects the air-fuel mixture produced by the air-fuel mixture chamber, and a holding member that holds the fuel injector and the air-fuel mixture injector. 
     In the vehicle, the drive wheel is driven by the power generated by the engine. 
     In the above-described fuel injection device, the fuel is injected by the fuel injector, and the injected fuel and air are mixed by the air-fuel mixture chamber, thereby producing the air-fuel mixture. The air-fuel mixture produced by the air-fuel mixture chamber is injected by the air-fuel mixture injector. The fuel injector and the air-fuel mixture injector are held by the holding member. 
     As described above, the fuel injector and the air-fuel mixture injector are integrated by the holding member, thereby eliminating the necessity of positioning the fuel injector and the air-fuel mixture injector. In addition, when the fuel injection device is attached to the engine, the fuel injector and the air-fuel mixture injector can be integrally handled. Furthermore, since the fuel injection device is provided separately from the engine, the fuel injection device can be attached to the assembled engine. Accordingly, workability of assembling the fuel injector and the air-fuel mixture injector is improved. 
     Moreover, a positional relationship between the fuel injector and the air-fuel mixture injector is fixed by the holding member, so that the positional relationship between the fuel injector and the air-fuel mixture injector is not affected by positions of other members of the engine. This improves positional accuracy of the fuel injector and the air-fuel mixture injector. 
     In addition, the fuel injector and the air-fuel mixture injector are integrally held by the holding member, so that rigidity of the fuel injection device is improved while performance for sealing the air-fuel mixture is improved. 
     Furthermore, the fuel injector and the air-fuel mixture injector are integrally held by the holding member, so that the configuration of the engine is simplified and made compact. 
     In the vehicle according to various preferred embodiments of the present invention, since the engine including the fuel injection device having the above-described configuration is used, the configuration is simplified while workability of assembling the vehicle becomes easy. Thus, the vehicle can be reduced in weight and cost. In addition, the positioning accuracy of the fuel injection device of the engine is improved, and a spray of the air-fuel mixture can be appropriately supplied to a combustion chamber. Thus, higher performance of the vehicle can be achieved. 
     According to a fuel injection device of various preferred embodiments of the present invention, positioning accuracy, assembly performance and rigidity are improved. 
     In addition, according to an engine and a vehicle of various preferred embodiments of the present invention, configurations thereof are simplified while reduction in weight and cost and higher performance can be achieved. 
     Other features, elements, characteristics, and advantages of the present invention will become more apparent from the following description of preferred embodiments of the present invention with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical sectional view of an engine according to a preferred embodiment of the present invention. 
         FIG. 2  is a transverse sectional view of the engine of  FIG. 1 . 
         FIGS. 3A and 3B  are perspective views showing a fuel injection device according a preferred embodiment of the present invention. 
         FIGS. 4A and 4B  are partially fragmented sectional views of the fuel injection device of  FIGS. 3A and 3B . 
         FIG. 5  is a perspective view showing a state where a cam cap is attached to a cylinder head. 
         FIG. 6  is a perspective view showing the configuration of the cam cap of  FIG. 5 . 
         FIGS. 7A and 7B  are detail views of the cam cap of  FIG. 6 . 
         FIG. 8  is a perspective view showing a state where the cylinder head, the cam cap and the fuel injection device are assembled. 
         FIG. 9  is a perspective view showing a state where the head cover is attached to the state shown in  FIG. 8 . 
         FIG. 10  is a schematic view of a motorcycle provided with the engine including the fuel injection device according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, description is made of a fuel injection device (injector) according to preferred embodiments of the present invention. 
     (1) Overall Engine 
     First, a brief description is provided of the configuration of an engine to which the fuel injection device according to the present preferred embodiment is attached. 
       FIG. 1  is a vertical sectional view of the engine  100  according to the present preferred embodiment. 
     As shown in  FIG. 1 , the engine  100  includes a cylinder  10 . A piston  11  is provided in the cylinder  10  so as to reciprocate up and down. 
     A cylinder head  12  is provided on the cylinder  10 . The cylinder  10  and the cylinder head  12  define a combustion chamber  12   a.    
     A cam cap  33  is mounted on the cylinder head  12  by knock pins  21 . An upper portion of the cylinder head  12  is covered with a head cover  13  made of aluminum, magnesium, light alloy, fiber materials, resin or the like, for example, with an elastic member  41  made of rubber, for example, sandwiched therebetween. Note that the configuration of the cam cap  33  will be described later. 
     An intake port  20  is arranged so as to obliquely extend downward from one side of the cylinder head  12  toward its center. 
     A throttle body (not shown) is arranged so as to be connected upstream of the intake port  20  of the cylinder head  12 . The throttle body and a funnel (not shown) attached to the throttle body constitute an intake pipe. Note that a throttle valve (not shown) is provided in the throttle body so as to turn around a horizontal axis that crosses a central axis of the intake port  20 . 
     An intake valve  14  is provided at a lower end opening of the intake port  20 . The intake valve  14  includes a valve head  14   a . This intake valve  14  is biased by springs  16  in such a direction that the valve head  14   a  closes the lower end opening of the intake port  20  (in an obliquely upward direction). An intake cam  18  is rotatably provided at an upper end of the intake valve  14 . The intake cam  18  rotates to open/close the intake valve  14 . 
     An exhaust port  32  is arranged so as to extend downward from the other side of the cylinder head  12  toward its center. 
     An exhaust valve  15  is provided at a lower end opening of the exhaust port  32 . This exhaust valve  15  includes a valve head  15   a . The exhaust valve  15  is biased by springs  17  in such a direction that the valve head  15   a  closes the lower end opening of the exhaust port  32  (in an obliquely upward direction). An exhaust cam  19  is rotatably provided at an upper end of the exhaust valve  15 . The exhaust cam  19  rotates to open/close the exhaust valve  15 . 
     In  FIG. 1 , a fuel injection device  1  that injects fuel is arranged so as to extend toward inside of the combustion chamber  12   a  through a hole  13   a , described later in  FIG. 2 , provided at the center of the head cover  13 . Note that details of the configuration of the fuel injection device  1  will be described later. 
       FIG. 2  is a transverse sectional view of the engine  100  of  FIG. 1 . 
     As shown in  FIG. 2 , the hole  13   a  into which the fuel injection device  1  is inserted is provided in the head cover  13 . 
     Here, in the present preferred embodiment, the fuel injection device  1  is provided through the hole  13   a  of the head cover  13  such that the tip thereof is in communication with the combustion chamber  12   a  while an upper portion thereof is fixed on the cam cap  33 , described later. Details will be described later. Note that the cam cap  33  is used for fixing camshafts to which the intake cam  18  and the exhaust cam  19  are attached, respectively, and not shown in  FIG. 2 . The cam cap  33  will be described later. 
     Moreover, an ignition plug  2  is arranged so as to be in communication with the combustion chamber  12   a  in  FIG. 2 . 
     (2) The Configuration of the Fuel Injection Device 
     Next, the fuel injection device  1  according to the present preferred embodiment is described with reference to the drawings.  FIGS. 3A and 3B  are perspective views showing the fuel injection device  1  according to the present preferred embodiment.  FIG. 3A  shows disassembled components of the fuel injection device  1 , and  FIG. 3B  shows the overall fuel injection device  1  into which the components are assembled. 
     As shown in  FIG. 3A , the fuel injection device  1  according to the present preferred embodiment includes an air-fuel mixture injector  3 , a fuel supplier  4 , a fuel injection device holder  5 , an insert piece  6 , a fuel introducer  7  and an air introducer  8  as the components. 
     The fuel injection device holder  5  has an air-fuel mixture chamber  5   a  that is provided in the inside of the fuel injection device holder  5  and produces an air-fuel mixture by mixing supplied fuel and air, and includes a mixer  51  at its one end and a connector  5   b  at its other end. The fuel introducer  7  and the air introducer  8  are connected to the connector  5   b , respectively, with the insert piece  6  sandwiched therebetween. Note that the fuel introducer  7  is connected to a fuel supply source (not shown) through a pipe (not shown), and the air introducer  8  is connected to an air supply source (not shown) through a pipe (not shown). 
     In addition, the fuel injection device holder  5  includes an air supply passage  5   c  that introduces air introduced from the air introducer  8  into the air-fuel mixture chamber  5   a  while extending between the air-fuel mixture chamber  5   a  and the connector  5   b . That is, the air supply passage  5   c  through which air passes and the air-fuel mixture chamber  5   a  are integrally formed. The air-fuel mixture injector  3  is attached to one end of the mixer  51 . This allows the air-fuel mixture injector  3  and the fuel supplier  4  to be integrated through the fuel injection device holder  5 . 
     The fuel supplier  4  is preferably tubular, and the fuel is introduced into the tube to be supplied to the air-fuel mixture chamber  5   a  within the mixer  51 . Moreover, one end of the fuel supplier  4  is attached to the other end of the mixer  51 , and the other end of the fuel supplier  4  is attached to the connector  5   b . That is, the fuel supplier  4  through which the fuel passes and the air-fuel mixture chamber  5   a  preferably are separately formed. 
     The air-fuel mixture injector  3  includes a wiring connector  3   a , and the fuel supplier  4  includes a wiring connector  4   a.    
     As shown in  FIG. 3B , the fuel injection device  1  according to the present preferred embodiment is a unit into which the fuel supplier  4  for supplying the fuel and the fuel injection device holder  5  for supplying air are integrally formed. 
       FIGS. 4A and 4B  are partially fragmented sectional views of the fuel injection device  1  of  FIG. 3 .  FIG. 4A  and  FIG. 4B  show vertical sectional views of the fuel injection device  1  in directions that are perpendicular to each other. Note that some of the components are not shown in  FIG. 4A . 
     As shown in  FIG. 4A , the connector  5   b  of the fuel injection device  1  includes two fixed portions  52  that project in a direction vertical to a direction in which the fuel introducer  7  and the air introducer  8  are attached. 
     The fixed portions  52  are fixed to the cam cap  33 , described later, by bolts B 1 . As described above, the fuel injection device  1  can be positioned only by fixing the fixed portions  52  of the fuel injection device  1  by the bolts B 1  Details will be described later. 
     In  FIG. 4B , a fuel introduction passage  7   a  is formed within the fuel introducer  7 , and an air introduction passage  8   a  is formed within the air introducer  8 . This air introduction passage  8   a  is in communication with the air supply passage  5   c , and air flowing into the air introduction passage  8   a  and the air supply passage  5   c  is supplied to the air-fuel mixture chamber  5   a.    
     As shown in  FIG. 4B , the fuel supplier  4  includes a fuel injection valve  4   b  at its downstream end and includes a fuel supply port  4   c , to which the fuel is supplied, at its upstream end. The air-fuel mixture injector  3  includes an air-fuel mixture injection valve  3   b  at its downstream end. 
     In the present preferred embodiment, the fuel injection valve  4   b  and air-fuel mixture injection valve  3   b  preferably are coaxially arranged. Thus, miniaturization is achieved while the mixture of fuel and air in the air-fuel mixture chamber  5   a  is efficiently injected from the air-fuel mixture injection valve  3   b.    
     Furthermore, the air-fuel mixture chamber  5   a  is provided downstream of the fuel supplier  4 , and the air-fuel mixture injector  3  is provided downstream of the air-fuel mixture chamber  5   a.    
     As described above, the air-fuel mixture chamber  5   a  is provided between the fuel supplier  4  and the air-fuel mixture injector  3 , so that the fuel supplier  4 , the air-fuel mixture chamber  5  and the air-fuel mixture injector  3  are aligned. This allows the configuration to be simplified and miniaturized. Moreover, the air-fuel mixture is further efficiently produced in the air-fuel mixture chamber  5   a  while the produced air-fuel mixture is further efficiently injected from the air-fuel mixture injection valve  3   b  of the air-fuel mixture injector  3 . 
     Note that opening/closing operations of the air-fuel mixture injection valve  3   b  are controlled by a controller (not shown) through a wiring (not shown) connected to the wiring connector  3   a , and opening/closing operations of the fuel injection valve  4   b  are controlled by the controller through a wiring (not shown) connected to the wiring connector  4   a.    
     (3) The Configuration of the Cam Cap 
     Next, description is made of the cam cap  33  to which the fuel injection device  1  according to the present preferred embodiment is fixed. 
       FIG. 5  is a perspective view showing a state where the cam cap  33  is attached to the cylinder head  12 . 
     As shown in  FIG. 5 , the cam cap  33  is attached to the upper portion of the cylinder head  12  preferably by a plurality of bolts B 2 . 
     Moreover, an insertion hole  22  into which the ignition plug  2  is inserted is provided at a side of the cylinder head  12 . Note that the ignition plug  2  is not shown in  FIG. 5 . 
     Next, the configuration of the cam cap  33  is described while referring to the drawings.  FIG. 6  is a perspective view showing the configuration of the cam cap  33  of  FIG. 5 . 
     As shown in  FIG. 6 , the cam cap  33  includes a fuel injection device fixing base  34 . 
     The fuel injection device fixing base  34  includes a fixed portion attachment elements  34   a  and an opening  34   b  having an elongate shape. The fixed portions  52  of the fuel injection device  1  of  FIG. 4A  are fixed to the fixed portion attachment elements  34   a  by the bolts B 1  while the fuel injection device  1  is inserted into the opening  34   b.    
     In addition, the fuel injection device fixing base  34  includes camshaft fixing portions  35  that fix the camshafts of  FIG. 6 . In the present preferred embodiment, two of the camshaft fixing portions  35  are preferably provided at each side of the fuel injection device fixing base  34  so as to be vertical to a longitudinal direction of the opening  34   b  having the elongated shape. In such a configuration, one camshaft (not shown) is fixed by the two camshaft fixing portions  35  provided at one side, and another camshaft (not shown) is fixed by the two camshaft fixing portions  35  provided at the other side. Note that the fuel injection device fixing base  34  and the camshaft fixing portions  35  preferably are integrally formed by casting or other suitable processing in the present preferred embodiment. 
     Furthermore, the camshaft fixing portions  35  include a plurality of (for example, four in  FIG. 6 ) screws  35   a  for attaching the head cover  13  of  FIG. 1  to the camshaft fixing portions  35  and a plurality of (for example, eight in  FIG. 6 : partially not shown) holes  35   b  into which the bolts B 2  are inserted when the camshaft fixing portions  35  are attached to the cylinder head  12  of  FIG. 5 . 
       FIGS. 7A and 7B  are detail views of the cam cap  33  of  FIG. 6 .  FIG. 7A  is a top view of the cam cap  33 , and  FIG. 7B  is a sectional view taken along the line A-A of the cam cap  33  in  FIG. 7A . 
     As shown in  FIG. 7B , each of the camshaft fixing portions  35  of the cam cap  33  includes an abutment portion  35   c , having a semi-circular cross section, which abuts against the camshaft. These abutment portions  35   c  abut against surfaces of the camshafts, respectively, so that the camshafts are fixed to the cam cap  33 . 
     (4) Assembly (ASSY) State 
     Next, description is made of assembly of the cylinder head  12 , the head cover  13 , the cam cap  33  and the fuel injection device  1 . 
       FIG. 8  is a perspective view showing a state where the cylinder head  12 , the cam cap  33  and the fuel injection device  1  are assembled.  FIG. 9  is a perspective view showing a state where the head cover  13  is attached to the state shown in  FIG. 8 . Note that the camshafts are not shown in  FIG. 8 . 
     As shown in  FIG. 8 , first, the cam cap  33  is attached to the upper portion of the cylinder head  12  by the plurality of bolts B 2 . Although the fuel injection device  1  is not assembled at this stage in the sequence of the assembly, it is shown in  FIG. 8  for easier understanding. 
     Then, the head cover  13  shown in  FIG. 9  is attached to the cam cap  33  by a plurality of bolts B 3 . The head cover  13  is provided with a plurality of holes corresponding to the screws  35   a  of the cam cap  33 , and attached to the camshaft fixing portions  35  of the cam cap  33  by the plurality of bolts B 3  through these holes. 
     In the present preferred embodiment, the elastic member  41  such as rubber, for example, is provided between the cylinder head  12  and the head cover  13 . In this manner, the cylinder head  12  and the head cover  13  abut against each other with the elastic member  41  sandwiched therebetween, so that the head cover  13  absorbs vibrations while insulating sound (radiated sound, for example) generated by the fuel injection device  1  and a valve driving device (not shown) and so on. Such a configuration provides sound insulation and vibration absorption. 
     In  FIG. 9 , the head cover  13  includes the hole  13   a  into which the fuel injection device  1  is inserted as described in  FIG. 1 . 
     Next, the fuel injection device  1  is inserted into the hole  13   a  while the fixed portions  52  of the fuel injection device  1  are attached to the fixed portion attachment elements  34   a  ( FIG. 6 ) of the cam cap  33  below the head cover  13  by the bolts B 1  in the above-described configuration. 
     (5) Effects of the Present Preferred Embodiment 
     (5-1) Effects Produced by the Configuration of the Fuel Injection Device 
     In the present preferred embodiment, the fuel supplier  4  and the air-fuel mixture injector  3  are held by the fuel injection device holder  5 . 
     As described above, the fuel supplier  4  and the air-fuel mixture injector  3  are integrated through the fuel injection device holder  5 , thereby eliminating the necessity of positioning the fuel supplier  4  and the air-fuel mixture injector  3 . 
     In addition, the fuel supplier  4  and the air-fuel mixture injector  3  can be integrally handled when the fuel injection device  1  is attached to the engine  100 . Furthermore, since the fuel injection device  1  is provided separately from the engine  7 , the fuel injection device  1  can be attached to the assembled engine  100 . Accordingly, workability of assembling the fuel supplier  4  and the air-fuel mixture injector  3  is improved. 
     Moreover, since a positional relationship between the fuel supplier  4  and the air-fuel mixture injector  3  is fixed by the fuel injection device holder  5 , the positional relationship between the fuel supplier  4  and the air-fuel mixture injector  3  is not affected by positions of other members in the engine  100 . This improves positional accuracy of the fuel supplier  4  and the air-fuel mixture injector  3 . 
     Furthermore, the fuel supplier  4  and the air-fuel mixture injector  3  are integrally held by the fuel injection device holder  5 , so that rigidity of the fuel injection device  1  is improved. 
     In addition, the fuel supplier  4  and the air-fuel mixture injector  3  are integrally held by the fuel injection device holder  5 , so that the configuration is simplified and made compact. 
     Moreover, in the present preferred embodiment, the fuel injection device holder  5  has the air supply passage  5   c  through which air is supplied to the air-fuel mixture chamber  5   a , thereby eliminating the necessity of additionally arranging the air supply passage  5   c  within the engine  100 . This simplifies the internal configuration of the engine  100  while improving workability of assembling. This also improves sealing performance of the air supply passage  5   c  and the air-fuel mixture chamber  5   a.    
     Furthermore, the air supply passage  5   c  of the fuel injection device holder  5  is arranged so as to extend from the air-fuel mixture chamber  5   a  and along a side surface of the fuel supplier  4 , so that the air supply passage  5   c  can be miniaturized and made compact. 
     In addition, the fuel supplier  4  includes the fuel injection valve  4   b  at its tip on the side of the air-fuel mixture chamber  5   a  and the fuel supply port  4   c  at its rear end, so that the fuel can be easily supplied from the outside of the head cover  13  of the engine  100  into the fuel supply port  4   c . This prevents the internal configuration of the engine  100  from being complicated. 
     Moreover, the air-fuel mixture chamber  5   a  is provided in a space surrounded by the tip of the fuel supplier  4 , the air-fuel mixture injector  3  and the fuel injection device holder  5 , so that the configuration is further simplified. This allows the configuration to be further miniaturized and made compact. 
     (5-2) Effects Produced by Fixing the Fuel Injection Device to the Cam Cap 
     In the present preferred embodiment, first, the cam cap  33  is mounted on the cylinder head  12  by the plurality of bolts B 2  with the knock pins  21  inserted. Thus, positioning accuracy of the cam cap  33  with respect to the cylinder head  12  is ensured. 
     As described above, the fuel injection device  1  is then attached to the fuel injection device fixing base  34  of the cam cap  33 , of which positioning accuracy is ensured, by the plurality of bolts B 1 . Such a configuration improves positioning accuracy of the fuel injection device  1  and causes the fuel injection device  1  to be more rigidly attached. 
     Moreover, when the fuel injection device  1  is attached to the fuel injection device fixing base  34  of the cam cap  33 , the fuel injection device  1  is inserted into the hole  13   a  provided in the head cover  13  that is previously attached to the cylinder head  12 . As described above, the hole  13   a  is provided in the head cover  13 , so that the fuel injection device  1  can be attached to the cylinder head  12  through the cam cap  33 . 
     Such a configuration does not require accuracy of attaching the head cover  13  to the cylinder head  12 , unlike conventional configurations. Thus, the fuel injection device  1  is attached to the fuel injection device fixing base  34  of the cam cap  33 , so that the positioning accuracy of the fuel injection device  1  is improved. In addition, an injector housing and the like that hold the fuel injection device  1  are not provided in the head cover  13 , thus simplifying the configuration and reducing the head cover  13  in weight. 
     Furthermore, in the present preferred embodiment, it is not necessary to ensure the positioning accuracy of the head cover  13  with respect to the cylinder head  12 , unlike conventional techniques, thereby eliminating the necessity of firmly fixing the head cover  13  to the cylinder head  12  by a knock pin and the like. Utilizing such a configuration, the elastic member  41  made of rubber and the like is provided between the cylinder head  12  and the head cover  13 . Accordingly, vibrations are absorbed by the head cover  13  while sound (radiated sound, for example) generated by the fuel injection device  1 , the valve driving device (not shown) and so on is insulated by the head cover  13 . Thus, sound insulation and vibration absorption can be realized. 
     (6) Motorcycle Provided with the Engine Including the Fuel Injection Device 
       FIG. 10  is a schematic view of a motorcycle provided with the engine  100  including the fuel injection device  1  according the above-described preferred embodiment. 
     As shown in  FIG. 10 , in the motorcycle  200 , a head  61  is provided at the front of a main body  60 . The head  61  is provided with a front fork  62  that is swingable rightward and leftward. 
     A front wheel  63  is rotatably supported at a lower end of the front fork  62 . The head  61  has a handle  64  attached to its upper end. 
     A main seat  65   a  and a tandem seat  65   b  are provided on the main body  60 . Moreover, the engine  100  is provided below the main body  60 . A rear wheel  66  is rotatably supported by the engine  100 , a rear arm (not shown) and so on. The rear wheel  66  is driven by power of the engine  100 . Note that a storage box  67  may be preferably provided within the main body  60  below the main seat  65   a  and the tandem seat  65   b.    
     In the motorcycle  200  of  FIG. 10 , the engine  100  having the simplified configuration while including the fuel injection device  1  according to the above-described present preferred embodiment is preferably used, thereby reducing fuel consumption and exhaust gas. 
     In addition, vibrations and radiated sound are reduced in the motorcycle  200 . This allows a rider to comfortably ride on the motorcycle. 
     (7) Other Preferred Embodiments 
     While description is made of a case where the fuel injection device of the present invention is preferably applied to a motorcycle in the above-described preferred embodiment, the fuel injection device is applicable similarly to vehicles such as a three-wheeled motor vehicle and a four-wheeled motor vehicle. 
     While description is made of an example in which the fuel injection device fixing base  34  preferably is integrally formed into the cam cap  33  in the above-described preferred embodiment, the present invention is not limited to this. The fuel injection device fixing base  34  and the cam cap  33  may be provided separately from each other. 
     While description is made of an example in which the cylinder head  12  and the cam cap  33  preferably are configured separately from each other in the above-described preferred embodiment, the present invention is not limited to this. The cylinder head  12  and the cam cap  33  may be integrally formed. 
     Furthermore, the head cover  13  may be configured so as to be detached without detaching the fuel injection device  1  or the fuel introducer  7  and the air introducer  8 . 
     In this case, the size of the hole  13   a  is suitably changed such that the fuel introducer  7  and the air introducer  8  pass through the hole  13   a  of the head cover  13  at the time of detaching the head cover  13 . 
     (8) Correspondences Between Elements Recited in Claims and Elements in Preferred Embodiments 
     In the following paragraph, non-limiting examples of correspondences between various elements recited in the claims below and those described above with respect to various preferred embodiments of the present invention are explained. 
     In the above-described preferred embodiment, the fuel supplier  4  and the fuel injection valve  4   b  are examples of a fuel injector, the air-fuel mixture injector  3  and the air-fuel mixture injection valve  3   b  are examples of an air-fuel mixture injector, the fuel injection device holder  5  is an example of a holding member, the fuel supply port  4   c  is an example of a supply port, and the rear wheel  66  is an example of a drive wheel. 
     As the elements recited in the claims, various other elements having the structure or function as recited in the claims may be employed. 
     The present invention is applicable to various types of vehicles and the like including an engine such as a motorcycle and a four-wheeled motor vehicle. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.