Abstract:
A common-rail fuel injection device for an internal combustion engine, including fuel injection valves each having two fuel supply ports, is known as a fuel injection device for suppressing temporary decrease of a fuel pressure immediately after the end of fuel injection from the fuel injection valve. Even in this fuel injection device, the fuel injection pressure may fluctuate immediately after the end of fuel injection, thereby causing changes of amount and particle diameter of injected fuel. A common rail is connected to one fuel supply port of the fuel injection valve, whereas another fuel injection valve, which is non-contiguous in the order of combustions, is connected to the other fuel supply port by an injection-valve connection pipe.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a common-rail fuel injection device for an internal combustion engine. 
         [0003]    2. Description of the Related Art 
         [0004]    A common-rail fuel injection device is known as a fuel injection device for an internal combustion engine (hereinafter also referred to simply as “engine”). In the common rail system, fuel pressurized by a fuel supply pump (supply pump) is accumulated in a common rail. The pressurized fuel is supplied from the common rail to fuel injection valves through fuel supply pipes (fuel injection pipes). 
         [0005]    Thus, at the time of fuel injection from the fuel injection valve, the fuel injection pressure of the fuel to be injected into each cylinder (combustion chamber) is increased so that the particle diameter of the fuel injected into the cylinder is reduced. As a result, the vaporization or atomization rate of the fuel injected into the combustion chamber is increased so that complete combustion is promoted, thereby reducing unburned substances contained in exhaust gas (such as hydrocarbon and carbon monoxide). 
         [0006]    In addition, the volume of the fuel accumulated in the common rail under the pressurized state is relatively large, and hence the decrease amount of the “pressure of the fuel supplied to the fuel injection valve (injection-valve fuel pressure)” is small immediately after the end of fuel injection. Therefore, the fuel injection can be repeated within a short period of time, thereby being capable of achieving multi-stage injection for injecting the fuel into a single cylinder a plurality of times in one cycle (sequential fuel injection involving pre-injection, main injection, after-injection, and post-injection). 
         [0007]    Even in the common-rail fuel injection device, however, the injection-valve fuel pressure is temporarily decreased to some extent when the fuel is injected. As a result, when further fuel injection is performed immediately after the end of fuel injection (for example, when second pre-injection is performed after first pre-injection), the actual fuel injection amount may become smaller than the expected fuel injection amount. In addition, the particle diameter of the injected fuel may become larger. 
         [0008]    In view of the above, one of the related-art common-rail fuel injection devices (hereinafter also referred to as “related-art device”) is applied to an engine including four cylinders, and includes four fuel injection valves each having two fuel supply ports and being arranged for a corresponding one of the cylinders. 
         [0009]    In this related-art device, one of the two fuel supply ports of the first fuel injection valve is directly connected to a common rail through a fuel supply pipe, whereas the other one of the fuel supply ports of the first fuel injection valve is directly connected to one of the two fuel supply ports of the second fuel injection valve through an injection-valve connection pipe. The other one of the fuel supply ports of the second fuel injection valve is directly connected to one of the two fuel supply ports of the third fuel injection valve through an injection-valve connection pipe. The other one of the fuel supply ports of the third fuel injection valve is directly connected to one of the two fuel supply ports of the fourth fuel injection valve through an injection-valve connection pipe. The other one of the fuel supply ports of the fourth fuel injection valve is directly connected to the common rail through a fuel supply pipe. Thus, each fuel injection valve injects the fuel supplied through the two fuel supply ports into the cylinder (see, for example, International Patent WO2011/085858A). 
         [0010]    According to the related-art device, the pressurized fuel is supplied to each fuel injection valve through the two fuel supply ports of each fuel injection valve, thereby being capable of reducing the magnitude of the decrease amount of the fuel injection pressure (injection-valve fuel pressure) immediately after the end of fuel injection as compared to a case where the fuel injection valve has one fuel supply port alone. 
         [0011]    Even in the related-art device, however, the injection-valve fuel pressure is decreased to some extent immediately after the end of fuel injection, and is increased afterwards. As a result, the injection-valve fuel pressure fluctuates over time. The fluctuation of the injection-valve fuel pressure (hereinafter also referred to simply as “fuel pressure fluctuation”) propagates to another fuel injection valve through the fuel in the injection-valve connection pipe. As a result, the amount of fuel injected in actuality may become significantly different from the expected amount of fuel, or the particle diameter of the injected fuel may become larger. 
         [0012]    Now, the above-mentioned fuel pressure fluctuation and its influence are further described with reference to an example of the related-art device having a schematic configuration illustrated in  FIG. 9 . 
         [0013]    The related-art device of  FIG. 9  includes a common rail  91  and a first fuel injection valve  92   a  to a fourth fuel injection valve  92   d.  The common rail  91  and the first fuel injection valve  92   a  are connected by a first fuel supply pipe  93   a.  The common rail  91  and the fourth fuel injection valve  92   d  are connected by a second fuel supply pipe  93   b.    
         [0014]    The first fuel injection valve  92   a  and the second fuel injection valve  92   b  are connected by a first injection-valve connection pipe  94   e.  The second fuel injection valve  92   b  and the third fuel injection valve  92   c  are connected by a second injection-valve connection pipe  94   b.  The third fuel injection valve  92   c  and the fourth fuel injection valve  92   d  are connected by a third injection-valve connection pipe  94   c.    
         [0015]      FIG. 4  is a graph for showing results of measurement conducted by the inventors of the present invention on “how the fuel pressure fluctuation caused by the fuel injection from the second fuel injection valve  92   b  propagates to the first fuel injection valve  92   a ” when the fuel injection is performed in an order of the first fuel injection valve  92   a,  the third fuel injection valve  92   c,  the fourth fuel injection valve  92   d,  and the second fuel injection valve  92   b.    
         [0016]    The solid line Lp 1  of  FIG. 4  indicates a change of the injection-valve fuel pressure of the second fuel injection valve  92   b  at the time of performing fuel injection from the second fuel injection valve  92   b.  The solid line Lp 2  of  FIG. 4  indicates a change of the injection-valve fuel pressure of the first fuel injection valve  92   a  at that time. As understood from the ellipse Ce 1  to the ellipse Ce 4  of  FIG. 4 , the injection-valve fuel pressure of the first fuel injection valve  92   a  fluctuates along with the fuel injection from the second fuel injection valve  92   b.    
         [0017]    Therefore, for example, when the timing of post-injection from the second fuel injection valve  92   b  and the timing of main injection from the first fuel injection valve  92   a  are close to each other (see  FIG. 2 ), the amount of fuel injected from the first fuel injection valve  92   a  in actuality may become significantly different from the expected amount of fuel. Further, when the fuel is injected from the first fuel injection valve  92   a  at a low injection-valve fuel pressure of the first fuel injection valve  92   a  (that is, at a trough of the fuel pressure fluctuation), the particle diameter of the injected fuel may become larger. 
       SUMMARY OF THE INVENTION 
       [0018]    The present invention has been made to solve the above-mentioned problems, and it is therefore one of objects of the present invention to provide a fuel injection device for an internal combustion engine, which is capable of suppressing influence of a fuel pressure fluctuation caused along with fuel injection from a certain fuel injection valve on “fuel injection from another fuel injection valve connected to the fuel injection valve by an injection-valve connection pipe”. 
         [0019]    A fuel injection device for an internal combustion engine according to the present invention for achieving the above-described object (hereinafter also referred to as “device of the present invention”) is applied to a multi-cylinder internal combustion engine with an even number of cylinders including four or more cylinders, the fuel injection device including: a common rail ( 14 ) to which pressurized fuel is to be supplied; a plurality of fuel injection valves ( 11   a  to  11   d ); a plurality of fuel supply pipes ( 12   a  to  12   d ); and a plurality of injection-valve connection pipes ( 13   a  and  13   b ). 
         [0020]    Each of the plurality of fuel injection valves has a first supply port ( 15   a  to  15   d ) and a second supply port ( 16   a  to  16   d ) that communicates to the first supply port, and is configured to inject the pressurized fuel, which is supplied to each of the first supply port and the second supply port, to a corresponding one of the even number of cylinders. 
         [0021]    Each of the plurality of fuel supply pipes directly connects the first supply port of the each of the plurality of fuel injection valves and the common rail. 
         [0022]    Each of the plurality of injection-valve connection pipes directly connects the second supply ports of a pair of the plurality of fuel injection valves provided to a pair of the cylinders, which are non-contiguous in an order of combustions. 
         [0023]    The description “directly connects” herein means that no other fuel injection valve is interposed. Thus, an orifice may be interposed at the end of each of the fuel supply pipe and the injection-valve connection pipe and/or at a portion other than the end. 
         [0024]    When a combustion order has arrived for a cylinder to which a certain fuel injection valve (fuel injection valve A) is provided so that fuel injection from the fuel injection valve A is performed, the fuel pressure fluctuates in the fuel injection valve A. The fuel pressure fluctuation propagates to another fuel injection valve (fuel injection valve B) connected to the fuel injection valve A by the injection-valve connection pipe. 
         [0025]    The cylinder to which the fuel injection valve A is provided and the cylinder to which the fuel injection valve B is provided are non-contiguous in the order of combustions, and hence the cylinder whose combustion is performed after the fuel injection from the fuel injection valve A is a cylinder to which a fuel injection valve other than the fuel injection valve A and the fuel injection valve B is provided. In other words, a certain length of time is taken since the end of fuel injection from the fuel injection valve A until the start of fuel injection from the fuel injection valve B. 
         [0026]    Therefore, at the timing of the combustion for the cylinder to which the fuel injection valve B is provided, the fuel pressure fluctuation caused by the fuel injection from the fuel injection valve A is mitigated. Thus, according to the device of the present invention, it is possible to suppress the influence of the fuel pressure fluctuation caused along with the fuel injection from a certain fuel injection valve on the fuel injection from another fuel injection valve connected to the fuel injection valve by the injection-valve connection pipe. 
         [0027]    In one embodiment of the present invention, channel sectional areas and lengths of the plurality of fuel supply pipes are equal to each other, and channel sectional areas and lengths of the plurality of injection-valve connection pipes are equal to each other. 
         [0028]    The fuel pressure fluctuation caused along with the fuel injection corresponds to a compressional wave, which propagates through each of the fuel in the fuel supply pipe and the fuel in the injection-valve connection pipe as a medium. Further, the compressional wave is reflected at, for example, the end of the fuel supply pipe (connection portion between the fuel supply pipe and the common rail) and the end of the injection-valve connection pipe (connection portion between the injection-valve connection pipe and the fuel injection valve). 
         [0029]    Thus, when the channel sectional areas and/or the lengths of the fuel supply pipes and/or the injection-valve connection pipes vary, characteristics of the fuel pressure fluctuations (waveforms indicating changes of the injection-valve fuel pressures with respect to time) vary as well. For example,  FIG. 10  is a graph for showing results of measurement conducted by the inventors of the present invention on changes of the injection-valve fuel pressures after the fuel injection from the first fuel injection valve  92   a  to the fourth fuel injection valve  92   d  of the above-mentioned related-art device illustrated in  FIG. 9 . 
         [0030]    In  FIG. 10 , the crank angle of each cylinder is adjusted so that compression top dead centers of the cylinders to which the first fuel injection valve  92   a  to the fourth fuel injection valve  92   d  are provided, respectively, coincide with each other (the adjusted crank angle is also referred to as “reference crank angle” for convenience). As a result, in FIG,  10 , the first fuel injection valve  92   a  to the fourth fuel injection valve  92   d  start the fuel injection at the same crank angle (crank angle CAa), and finish the fuel injection at the same crank angle (crank angle CAb). As understood from the ellipse Ce 5  of  FIG. 10 , the characteristics of the fuel pressure fluctuations of the first fuel injection valve  92   a  to the fourth fuel injection valve  92   d  are significantly different from each other. 
         [0031]    Meanwhile, in the embodiment of the present invention, the channel sectional areas and the lengths of the plurality of fuel supply pipes are equal to each other, and the channel sectional areas and the lengths of the plurality of injection-valve connection pipes are equal to each other. Thus, as shown in the graph of  FIG. 3  similar to that of  FIG. 10 , the characteristics of the fuel pressure fluctuations of the plurality of fuel injection valves are similar to each other. 
         [0032]    For example, under the similar characteristics of the fuel pressure fluctuations, at the time of performing multi-stage injection, in which further fuel injection (second-stage injection) is performed after the fuel injection (first-stage injection), a map for predicting the amount of the change of the injection-valve fuel pressure at the injection timing of second-stage injection based on “an injection period of the first-stage injection, a period from the first-stage injection to the second-stage injection, an injection-valve fuel pressure at the time of first-stage injection, and other parameters” can be shared among all the fuel injection valves. Thus, according to the embodiment of the present invention, there is no need to adapt the maps to the respective fuel injection valves, thereby being capable of reducing the number of adaptation steps. 
         [0033]    The device of the present invention may be applied to an in-line four-cylinder engine constructed such that a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder are arrayed in line in the stated order, and that the combustions are performed in an order of the first cylinder, the third cylinder, the fourth cylinder, and the second cylinder,
       in which the plurality of fuel injection valves include:
           a first fuel injection valve ( 11   a ) provided to the first cylinder;   a second fuel injection valve ( 11   b ) provided to the second cylinder;   a third fuel injection valve ( 11   c ) provided to the third cylinder; and   a fourth fuel injection valve ( 11   d ) provided to the fourth cylinder, and   
           in which the plurality of injection-valve connection pipes include:
           a first connection pipe ( 13   a ) directly connecting the second supply port ( 16   a ) of the first fuel injection valve and the second supply port ( 16   d ) of the fourth fuel injection valve; and   a second connection pipe ( 13   b ) directly connecting the second supply port ( 16   b ) of the second fuel injection valve and the second supply port ( 16   c ) of the third fuel injection valve.   
               
 
         [0042]    Alternatively, the device of the present invention may be applied to an in-line six-cylinder engine constructed such that a first cylinder, a second cylinder, a third cylinder, a fourth cylinder, a fifth cylinder, and a sixth cylinder are arrayed in line in the stated order, and that the combustions are performed in an order of the first cylinder, the fifth cylinder, the third cylinder, the sixth cylinder, the second cylinder, and the fourth cylinder,
       in which the plurality of fuel injection valves include:
           a first fuel injection valve ( 31   a ) provided to the first cylinder;   a second fuel injection valve ( 31   b ) provided to the second cylinder;   a third fuel injection valve ( 31   c ) provided to the third cylinder;   a fourth fuel injection valve ( 31   d ) provided to the fourth cylinder;   a fifth fuel injection valve ( 31   e ) provided to the fifth cylinder; and   a sixth fuel injection valve ( 31   f ) provided to the sixth cylinder, and   
           in which the plurality of injection-valve connection pipes include:
           a first connection pipe ( 33   a ) directly connecting the second supply port ( 36   a ) of the first fuel injection valve and the second supply port ( 36   f ) of the sixth fuel injection valve;   a second connection pipe ( 33   b ) directly connecting the second supply port ( 36   b ) of the second fuel injection valve and the second supply port ( 36   e ) of the fifth fuel injection valve; and   a third connection pipe ( 33   c ) directly connecting the second supply port ( 36   c ) of the third fuel injection valve and the second supply port ( 36   d ) of the fourth fuel injection valve.   
               
 
         [0054]    Alternatively, the device of the present invention may be applied to an in-line six-cylinder engine constructed such that a first cylinder, a second cylinder, a third cylinder, a fourth cylinder, a fifth cylinder, and a sixth cylinder are arrayed in line in the stated order, and that the combustions are performed in an order of the first cylinder, the fourth cylinder, the second cylinder, the third cylinder, the sixth cylinder, and the fifth cylinder,
       in which the plurality of fuel injection valves include:
           a first fuel injection valve ( 31   a ) provided to the first cylinder;   a second fuel injection valve ( 31   b ) provided to the second cylinder;   a third fuel injection valve ( 31   c ) provided to the third cylinder;   a fourth fuel injection valve ( 31   d ) provided to the fourth cylinder;   a fifth fuel injection valve ( 31   e ) provided to the fifth cylinder; and   a sixth fuel injection valve ( 31   f ) provided to the sixth cylinder, and   
           in which the plurality of injection-valve connection pipes include:
           a first connection pipe ( 43   a ) directly connecting the second supply port ( 36   a ) of the first fuel injection valve and the second supply port of ( 36   c ) the third fuel injection valve;   a second connection pipe ( 43   b ) directly connecting the second supply port ( 36   b ) of the second fuel injection valve and the second supply port ( 36   e ) of the fifth fuel injection valve; and   a third connection pipe ( 43   c ) directly connecting the second supply port ( 36   d ) of the fourth fuel injection valve and the second supply port ( 36   f ) of the sixth fuel injection valve.   
               
 
         [0066]    Alternatively, the device of the present invention may be applied to a V-type six-cylinder engine constructed such that a first cylinder group having a first cylinder, a third cylinder, and a fifth cylinder arrayed in line in the stated order and a second cylinder group having a second cylinder, a fourth cylinder, and a sixth cylinder arrayed in line in the stated order are arranged to have a predetermined bank angle, and that the combustions are performed in an order of the first cylinder, the second cylinder, the third cylinder, the fourth cylinder, the fifth cylinder, and the sixth cylinder,
       in which the plurality of fuel injection valves include:
           a first fuel injection valve ( 51   a ) provided to the first cylinder;   a second fuel injection valve ( 51   b ) provided to the second cylinder;   a third fuel injection valve ( 51   c ) provided to the third cylinder;   a fourth fuel injection valve ( 51   d ) provided to the fourth cylinder;   a fifth fuel injection valve ( 51   e ) provided to the fifth cylinder; and   a sixth fuel injection valve ( 51   f ) provided to the sixth cylinder, and   
           in which the plurality of injection-valve connection pipes include:
           a first connection pipe ( 53   a ) directly connecting the second supply port ( 56   a ) of the first fuel injection valve and the second supply port of ( 56   d ) the fourth fuel injection valve;   a second connection pipe ( 53   b ) directly connecting the second supply port ( 56   b ) of the second fuel injection valve and the second supply port ( 56   e ) of the fifth fuel injection valve; and   a third connection pipe ( 53   c ) directly connecting the second supply port ( 56   c ) of the third fuel injection valve and the second supply port ( 56   f ) of the sixth fuel injection valve.   
               
 
         [0078]    Alternatively, the device of the present invention may be applied to a V-type six-cylinder engine constructed such that a first cylinder group having a first cylinder, a third cylinder, and a fifth cylinder arrayed in line in the stated order and a second cylinder group having a second cylinder, a fourth cylinder, and a sixth cylinder arrayed in line in the stated order are arranged to have a predetermined bank angle, and that the combustions are performed in an order of the first cylinder, the second cylinder, the third cylinder, the fourth cylinder, the fifth cylinder, and the sixth cylinder,
       in which the plurality of fuel injection valves include:
           a first fuel injection valve ( 51   a ) provided to the first cylinder;   a second fuel injection valve ( 51   b ) provided to the second cylinder;   a third fuel injection valve ( 51   c ) provided to the third cylinder;   a fourth fuel injection valve ( 51   d ) provided to the fourth cylinder;   a fifth fuel injection valve ( 51   e ) provided to the fifth cylinder; and   a sixth fuel injection valve ( 51   f ) provided to the sixth cylinder, and   
           in which the plurality of injection-valve connection pipes include:
           a first connection pipe ( 63   a ) directly connecting the second supply port ( 56   a ) of the first fuel injection valve and the second supply port ( 56   c ) of the third fuel injection valve;   a second connection pipe ( 63   b ) directly connecting the second supply port ( 56   b ) of the second fuel injection valve and the second supply port ( 56   e ) of the fifth fuel injection valve; and   a third connection pipe ( 63   c ) directly connecting the second supply port ( 56   d ) of the fourth fuel injection valve and the second supply port ( 56   f ) of the sixth fuel injection valve.   
               
 
         [0090]    In any of the above-mentioned embodiments (configurations), each of the plurality of injection-valve connection pipes directly connects the second supply ports of the pair of fuel injection valves provided to the pair of cylinders, which are non-contiguous in the order of combustions. Thus, it is possible to suppress the influence of the fuel pressure fluctuation caused along with the fuel injection from a certain fuel injection valve on the fuel injection from another fuel injection valve connected to the fuel injection valve by the injection-valve connection pipe. 
         [0091]    In the above description, the terms and/or reference symbols used in embodiments described later are enclosed in parentheses and assigned to the components of the present invention corresponding to the embodiments for easier understanding of the present invention. However, the constituent elements of the present invention are not limited to the embodiments defined by the terms and/or reference symbols. Other objects, other features, and accompanying advantages of the present invention are easily understandable from the description of the embodiments of the present invention to be given with reference to the following drawings, 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0092]      FIG. 1  is a schematic diagram of a fuel injection device for an internal combustion engine (first device) according to a first embodiment of the present invention. 
           [0093]      FIG. 2  is a time chart for illustrating fuel injection timings of fuel injection valves provided to the first device. 
           [0094]      FIG. 3  is a graph for showing changes of injection-valve fuel pressures of the fuel injection valves provided to the first device. 
           [0095]      FIG. 4  is a graph for showing changes of injection-valve fuel pressures of second fuel injection valves and first fuel injection valves, which are provided to a related-art device and the first device, respectively, along with fuel injection from the second fuel injection valves. 
           [0096]      FIG. 5  is a schematic diagram of a fuel injection device for an internal combustion engine according to a second embodiment of the present invention. 
           [0097]      FIG. 6  is a schematic diagram of a fuel injection device for an internal combustion engine according to a third embodiment of the present invention. 
           [0098]      FIG. 7  is a schematic diagram of a fuel injection device for an internal combustion engine according to a fourth embodiment of the present invention. 
           [0099]      FIG. 8  is a schematic diagram of a fuel injection device for an internal combustion engine according to a fifth embodiment of the present invention. 
           [0100]      FIG. 9  is a schematic diagram of the related-art device. 
           [0101]      FIG. 10  is a graph for showing changes of injection-valve fuel pressures of fuel injection valves provided to the related-art device. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0102]    Now, description is given of a fuel injection device for an internal combustion engine according to each of embodiments of the present invention with reference to the drawings. 
       First Embodiment 
       [0103]      FIG. 1  is a schematic illustration of a fuel injection device  10  for an internal combustion engine according to a first embodiment of the present invention (hereinafter also referred to as “first device”). The fuel injection device  10  is applied to an in-line four-cylinder, four-stroke cycle, and compression ignition diesel engine (not shown) (hereinafter also referred to simply as “engine”). 
         [0104]    The fuel injection device  10  includes a first fuel injection valve  11   a  to a fourth fuel injection valve  11   d , a first fuel supply pipe  12   a  to a fourth fuel supply pipe  12   d,  a first injection-valve connection pipe  13   a  and a second injection-valve connection pipe  13   b , a common rail  14 , and a first orifice  17   a  to a fourth orifice  17   d.    
         [0105]    The first fuel injection valve  11   a  to the fourth fuel injection valve  11   d  are provided to the four cylinders (not shown) (first cylinder to fourth cylinder) of the engine, respectively. The first cylinder to the fourth cylinder are arrayed in line in the stated order. Thus, the first fuel injection valve  11   a  to the fourth fuel injection valve  11   d  are arrayed in line in the stated order. 
         [0106]    The lengths of the first fuel supply pipe  12   a  to the fourth fuel supply pipe  12   d  are equal to each other. The channel sectional areas of the first fuel supply pipe  12   a  to the fourth fuel supply pipe  12   d  are uniform and equal to each other. 
         [0107]    The lengths of the first injection-valve connection pipe  13   a  and the second injection-valve connection pipe  13   b  are equal to each other. The channel sectional areas of the first injection-valve connection pipe  13   a  and the second injection-valve connection pipe  13   b  are uniform and equal to each other. 
         [0108]    The first fuel injection valve  11   a  has a first supply port  15   a  and a second supply port  16   a.  The first supply port  15   a  and the second supply port  16   a  communicate to each other at the inside of the first fuel injection valve  11   a.  When the first fuel injection valve  11   a  is opened, fuel supplied through the first supply port  15   a  and the second supply port  16   a  is injected into the first cylinder. 
         [0109]    The second fuel injection valve  11   b  has a first supply port  15   b  and a second supply port  16   b.  The first supply port  15   b  and the second supply port  16   b  communicate to each other at the inside of the second fuel injection valve  11   b . When the second fuel injection valve  11   b  is opened, fuel supplied through the first supply port  15   b  and the second supply port  16   b  is injected into the second cylinder. 
         [0110]    The third fuel injection valve  11   c  has a first supply port  15   c  and a second supply port  16   c.  The first supply port  15   c  and the second supply port  16   c  communicate to each other at the inside of the third fuel injection valve  11   c.  When the third fuel injection valve  11   e  is opened, fuel supplied through the first supply port  15   c  and the second supply port  16   c  is injected into the third cylinder. 
         [0111]    The fourth fuel injection valve  11   d  has a first supply port  15   d  and a second supply port  16   d.  The first supply port  15   d  and the second supply port  16   d  communicate to each other at the inside of the fourth fuel injection valve  11   d . When the fourth fuel injection valve  11   d  is opened, fuel supplied through the first supply port  15   d  and the second supply port  16   d  is Injected into the fourth cylinder. 
         [0112]    One end of each of the first fuel supply pipe  12   a  to the fourth fuel supply pipe  12   d  is connected to the common rail  14 . The first orifice  17   a  to the fourth orifice  17   d  are interposed between the first fuel supply pipe  12   a  to the fourth fuel supply pipe  12   d  and the common rail  14 , respectively. Each of the first orifice  17   a  to the fourth orifice  17   d  is provided for the purpose of preventing a pressure change (fluctuation) of the fuel in a corresponding one of the first fuel supply pipe  12   a  to the fourth fuel supply pipe  12   d  from propagating to the fuel in the common rail  14  to cause a pressure fluctuation of the fuel in the common rail  14 . 
         [0113]    The other end of the first fuel supply pipe  12   a  is connected to the first supply port  15   a  of the first fuel injection valve  11   a,  whereas one end of the first injection-valve connection pipe  13   a  is connected to the second supply port  16   a  of the first fuel injection valve  11   a.  The other end of the second fuel supply pipe  12   b  is connected to the first supply port  15   b  of the second fuel injection valve  11   b,  whereas one end of the second injection-valve connection pipe  13   b  is connected to the second supply port  16   b  of the second fuel injection valve  11   b.    
         [0114]    The other end of the third fuel supply pipe  12   c  is connected to the first supply port  15   c  of the third fuel injection valve  11   c,  whereas the other end of the second injection-valve connection pipe  13   b  is connected to the second supply port  16   c  of the third fuel injection valve  11   c.  The other end of the fourth fuel supply pipe  12   d  is connected to the first supply port  15   d  of the fourth fuel injection valve  11   d , whereas the other end of the first injection-valve connection pipe  13   a  is connected to the second supply port  16   d  of the fourth fuel injection valve  11   d.    
         [0115]    Thus, the fuel is supplied from the common rail  14  to the first fuel injection valve  11   a  through the first fuel supply pipe  12   a,  and is also supplied from the common rail  14  to the first fuel injection valve  11   a  through the fourth fuel supply pipe  12   d,  the fourth fuel injection valve  11   d , and the first injection-valve connection pipe  13   a.  Similarly, the fuel is supplied from the common rail  14  to the second fuel injection valve  11   b  through the second fuel supply pipe  12   b,  and is also supplied from the common rail  14  to the second fuel injection valve  11   b  through the third fuel supply pipe  12   c,  the third fuel injection valve  11   c,  and the second injection-valve connection pipe  13   b.    
         [0116]    The fuel is supplied from the common rail  14  to the third fuel injection valve  11   c  through the third fuel supply pipe  12   c,  and is also supplied from the common rail  14  to the third fuel injection valve  11   c  through the second fuel supply pipe  12   b,  the second fuel injection valve  11   b,  and the second injection-valve connection pipe  13   b.  The fuel is supplied from the common rail  14  to the fourth fuel injection valve  11   d  through the fourth fuel supply pipe  12   d,  and is also supplied from the common rail  14  to the fourth fuel injection valve  11   d  through the first fuel supply pipe  12   a,  the first fuel injection valve  11   a,  and the first injection-valve connection pipe  13   a.    
         [0117]    The fuel injection device  10  further includes a fuel tank  18 , a fuel supply pump  19 , a low-pressure pipe  19   a,  a high-pressure pipe  19   b,  and an ECU  20 . 
         [0118]    The fuel tank  18  stores the fuel (light oil) of the engine. The fuel supply pump  19  draws up the fuel in the fuel tank  18  through the low-pressure pipe  19   a,  and feeds the fuel under pressure to the common rail  14  through the high-pressure pipe  19   b.  Thus, the common rail  14  accumulates the fuel pressurized by the fuel supply pump  19 . The fuel supply pump  19  is actuated by a drive shaft (not shown) interlocking with a crankshaft of the engine. 
         [0119]    The ECU  20  is an electronic control unit, and includes a CPU  21 , a ROM  22 , and a RAM  23 . The CPU  21  sequentially executes a predetermined program (routine) to, for example, read data, perform numerical calculation, and output calculation results. The ROM  22  stores, for example, the program to be executed by the CPU  21  and lookup tables (maps). The RAM  23  stores the data temporarily. 
         [0120]    The ECU  20  is connected to a rail pressure sensor  24 , a first injection-valve fuel pressure sensor  25   a  to a fourth injection-valve fuel pressure sensor  25   d,  and a crank angle sensor  26  to receive signals from those sensors. 
         [0121]    The rail pressure sensor  24  detects a pressure of the fuel in the common rail  14  (rail pressure) to output a signal indicating a rail pressure Pa. 
         [0122]    The first injection-valve fuel pressure sensor  25   a  outputs a signal indicating a first injection-valve fuel pressure Pi 1 , which is a pressure of the fuel supplied to the first fuel injection valve  11   a  through the first supply port  15   a  and the second supply port  16   a  (that is, a fuel injection pressure). 
         [0123]    The second injection-valve fuel pressure sensor  25   b  outputs a signal indicating a second injection-valve fuel pressure Pi 2 , which is a pressure of the fuel supplied to the second fuel injection valve  11   b  through the first supply port  15   b  and the second supply port  16   b.    
         [0124]    The third injection-valve fuel pressure sensor  25   c  outputs a signal indicating a third injection-valve fuel pressure Pi 3 , which is a pressure of the fuel supplied to the third fuel injection valve  11   c  through the first supply port  15   c  and the second supply port  16   c.    
         [0125]    The fourth injection-valve fuel pressure sensor  25   d  outputs a signal indicating a fourth injection-valve fuel pressure Pi 4 , which is a pressure of the fuel supplied to the fourth fuel injection valve lid through the first supply port  15   d  and the second supply port  16   d.    
         [0126]    The crank angle sensor  26  generates a pulse for each rotation of the crankshaft of the engine by a given angle. The ECU  20  detects an engine rotation speed NE based on the pulse from the crank angle sensor  26 . Further, the ECU  20  acquires a crank angle CA of a specific cylinder provided to the engine based on the pulse from the crank angle sensor  26  and a pulse from a cam position sensor (not shown). 
         [0127]    The ECU  20  determines, for example, a target rail pressure Ptgt, a fuel injection amount, and a fuel injection timing for each cycle of the engine depending on the engine rotation speed NE, a required torque of the engine, a temperature of an exhaust gas purification catalyst provided to the engine, and other parameters. 
         [0128]    The ECU  20  controls the fuel supply pump  19  so that the rail pressure Pa becomes equal to the target rail pressure Ptgt. In addition, when any one of the first fuel injection valve  11   a  to the fourth fuel injection valve  11   d  has reached the fuel injection timing, the ECU  20  transmits a signal for opening the fuel injection valve so that the fuel is injected from the fuel injection valve. 
         [0129]      FIG. 2  is an illustration of examples of the fuel injection timings of the first fuel injection valve  11   a  to the fourth fuel injection valve  11   d.  Each of the first fuel injection valve  11   a  to the fourth fuel injection valve  11   d  performs pilot injection, first pre-injection, second pre-injection, main injection, after-injection, and post-injection for each cycle. When the temperature of the exhaust gas purification catalyst is sufficiently high, the after-injection and/or the post-injection are omitted. 
         [0130]    As understood from  FIG. 2 , the ECU  20  performs the fuel injection in an order of the first fuel injection valve  11   a,  the third fuel injection valve  11   c , the fourth fuel injection valve  11   d,  and the second fuel injection valve  11   b . In other words, the engine is constructed such that the combustions are performed in an order of the first cylinder, the third cylinder, the fourth cylinder, and the second cylinder. 
         [0131]    (Influence of Fuel Pressure Fluctuation in Fuel Injection Valve having Injected Fuel on Fuel Injection Amount and its Correction) 
         [0132]    Now, influence of a fuel pressure fluctuation in the fuel injection valve having injected the fuel on the fuel injection amount is described prior to description of actions and effects of the first device. 
         [0133]    Now, focus is placed on the first fuel injection valve  11   e . When the first fuel injection valve  11   a  is closed (when the fuel injection is not performed), the fuel is fed under pressure to the first fuel injection valve  11   a  through the first fuel supply pipe  12   a  and the first injection-valve connection pipe  13   a,  thereby maintaining a state in which the first injection-valve fuel pressure Pi 1  is substantially equal to the rail pressure Pa. When the fuel is injected from the first fuel injection valve  11   a,  however, the first injection-valve fuel pressure Pi 1  is decreased temporarily, and is increased afterwards. As a result, a fluctuation (fuel pressure fluctuation) occurs in such a manner that the first injection-valve fuel pressure Pi 1  is increased and decreased repeatedly. 
         [0134]    When the fuel is injected from the first fuel injection valve  11   a  again under the fluctuation of the first injection-valve fuel pressure Pi 1 , the amount of fuel injected in actuality may be changed depending on the first injection-valve fuel pressure Pi 1  at the time of fuel injection. That is, even under the same fuel injection period (open period), when the fuel is injected at a high first injection-valve fuel pressure Pi 1 , the amount of fuel injected in actuality becomes larger than in a case where the fuel is injected at a low first injection-valve fuel pressure Pi 1 . 
         [0135]    Therefore, when further fuel injection (second-stage injection) is performed after the fuel injection (first-stage injection) for the same cycle, the ECU  20  adjusts a fuel injection period of the second-stage injection. Specifically, the ECU  20  acquires (predicts) an estimated value of the first injection-valve fuel pressure Pi 1  at the start of second-stage injection by applying pressure parameters (that is, an injection period of the first-stage injection, a period from the end of first-stage injection to the start of second-stage injection, the first injection-valve fuel pressure Pi 1  at the start of first-stage injection, and other parameters) to a lookup table stored in advance which defines the relation between the first injection-valve fuel pressure Pi 1  at the start of second-stage injection and the pressure parameters. For convenience, this lookup table is also referred to as “fuel injection period adjustment map”. When the predicted first injection-valve fuel pressure Pi 1  at the start of second-stage injection is low, the ECU  20  sets the injection period of the second-stage injection to become longer than in a case where the first injection-valve fuel pressure Pi 1  is high. 
         [0136]    As described above, the channel sectional areas and the lengths of the first fuel supply pipe  12   a  to the fourth fuel supply pipe  12   d  are equal to each other, and the channel sectional areas and the lengths of the first injection-valve connection pipe  13   a  and the second injection-valve connection pipe  13   b  are equal to each other. Therefore, characteristics of the fluctuations of the first injection-valve fuel pressure Pi 1  to the fourth injection-valve fuel pressure Pi 4 , which are caused along with the fuel injection from the respective injection valves (pressure change with respect to time), are similar to each other. 
         [0137]    Specifically,  FIG. 3  is a graph for showing an example of the characteristics of the fluctuations of the first injection-valve fuel pressure Pi 1  to the fourth injection-valve fuel pressure Pi 4 . In the graph of  FIG. 3 , the crank angle CA on the horizontal axis is adjusted so that the fuel injection start timing of each of the first fuel injection valve  11   a  to the fourth fuel injection valve  11   d  becomes a timing corresponding to a crank angle CAa of each cylinder. As understood from  FIG. 3 , the characteristics of the fluctuations of the first injection-valve fuel pressure Pi 1  to the fourth injection-valve fuel pressure Pi 4  are similar to each other at a crank angle CAb at the end of fuel injection or subsequent crank angles. 
         [0138]    If the characteristics of the fluctuations of the first injection-valve fuel pressure Pi 1  to the fourth injection-valve fuel pressure Pi 4  are significantly different from each other (see  FIG. 10 ), the ECU  20  needs to store fuel injection period adjustment maps separately for the first injection-valve fuel pressure Pi 1  to the fourth injection-valve fuel pressure Pi 4 . However, the characteristics of the fluctuations of the first fuel injection valve  11   a  to the fourth fuel injection valve  11   d  are similar to each other, and hence the ECU  20  does not need to store the fuel injection period adjustment maps for the respective fuel injection valves. That is, the ECU  20  may refer to a common fuel injection period adjustment map when estimating the first injection-valve fuel pressure Pi 1  to the fourth injection-valve fuel pressure Pi 4 . In other words, according to the first device, there is no need to prepare the fuel injection period adjustment maps for the respective fuel injection valves, thereby being capable of reducing the number of adaptation steps greatly. Further, there is no need to store the fuel injection period adjustment maps in the ROM  22  for the respective fuel injection valves, thereby being capable of adopting a ROM  22  that is small in storage capacity by an amount corresponding to the respective fuel injection period adjustment maps. 
         [0139]    (Influence of Fuel Pressure Fluctuation Caused by Fuel Injection from Certain Fuel Injection Valve on Other Fuel Injection Valve) 
         [0140]    Next, description is given of influence of a fuel pressure fluctuation caused by fuel injection from a certain fuel injection valve on “fuel injection from another fuel injection valve”. As described above, the first fuel injection valve  11   a  and the fourth fuel injection valve  11   d  are connected to each other by the first injection-valve connection pipe  13   a.  Therefore, the fluctuation of the first injection-valve fuel pressure Pi 1  which is caused along with the fuel injection from the first fuel injection valve  11   a,  propagates to the fourth fuel injection valve  11   d  through the first injection-valve connection pipe  13   a.  That is, the fluctuation of the fourth injection-valve fuel pressure Pi 4  is caused by the fuel injection from the first fuel injection valve  11   a.    
         [0141]    Meanwhile, the combustions of the engine are performed in an order of the first cylinder, the third cylinder, the fourth cylinder, and the second cylinder. In other words, the third fuel injection valve  11   c  is a fuel injection valve that performs the fuel injection subsequently to the first fuel injection valve  11   a,  and the fourth fuel injection valve  11   d  performs the fuel injection subsequently to the third fuel injection valve  11   c.    
         [0142]    Thus, a certain length of time is taken since the end of fuel injection from the first fuel injection valve lie until the start of fuel injection from the fourth fuel injection valve lid for a certain cycle. As a result, at the start of fuel injection from the fourth fuel injection valve  11   d,  the fluctuation of the fourth injection-valve fuel pressure Pi 4 , which is caused along with the fuel injection from the first fuel injection valve  11   a , is mitigated. Therefore, there is no such phenomenon that the amount of fuel injected from the fourth fuel injection valve  11   d  becomes significantly different from the expected amount. 
         [0143]    Similarly, the fluctuation of the first injection-valve fuel pressure Pi 1  is caused along with the fuel injection from the fourth fuel injection valve  11   d , However, the second fuel injection valve  11   b  is a fuel injection valve that performs the fuel injection subsequently to the fourth fuel injection valve  11   d , and the first fuel injection valve  11   a  performs the fuel injection subsequently to the second fuel injection valve  11   b.  Thus, at the time of fuel injection from the first fuel injection valve  11   a,  the fluctuation of the first injection-valve fuel pressure Pi 1 , which is caused along with the fuel injection from the fourth fuel injection valve  11   d,  is mitigated. Therefore, there is no such phenomenon that the amount of fuel injected from the first fuel injection valve  11   a  becomes significantly different from the expected amount. 
         [0144]    Further, the second fuel injection valve  11   b  and the third fuel injection valve  11   c  are connected to each other by the second injection-valve connection pipe  13   b.  Therefore, the third injection-valve fuel pressure Pi 3  fluctuates due to the fuel injection from the second fuel injection valve  11   b , and the second injection-valve fuel pressure Pi 2  fluctuates due to the fuel injection from the third fuel injection valve  11   c.  However, the first fuel injection valve  11   a  is a fuel injection valve that performs the fuel injection subsequently to the second fuel injection valve  11   b,  and the third fuel injection valve  11   c  is a fuel injection valve that performs the fuel injection subsequently to the first fuel injection valve  11   a.    
         [0145]    Thus, at the time of fuel injection from the third fuel injection valve  11   c , the fluctuation of the third injection-valve fuel pressure Pi 3 , which is caused along with the fuel injection from the second fuel injection valve  11   b,  is mitigated. Therefore, there is no such phenomenon that the amount of fuel injected from the third fuel injection valve  11   c  becomes significantly different from the expected amount. 
         [0146]    Similarly, the fourth fuel injection valve  11   d  is a fuel injection valve that performs the fuel injection subsequently to the third fuel injection valve  11   c,  and the second fuel injection valve  11   b  is a fuel injection valve that performs the fuel injection subsequently to the fourth fuel injection valve  11   d.  Thus, at the time of fuel injection from the second fuel injection valve  11   b,  the fluctuation of the second injection-valve fuel pressure Pi 2 , which is caused along with the fuel injection from the third fuel injection valve  11   c,  is mitigated. Therefore, there is no such phenomenon that the amount of fuel injected from the second fuel injection valve  11   b  becomes significantly different from the expected amount. 
         [0147]      FIG. 4  is a graph for showing that the fluctuation of the injection-valve fuel pressure is suppressed as described above according to the first device. More specifically, the broken line Ln 1  of  FIG. 4  indicates an example of a change of the second injection-valve fuel pressure Pi 2  at the time of fuel injection from the second fuel injection valve  11   b.  In addition, the broken line Ln 2  of  FIG. 4  indicates an example of a change of the first injection-valve fuel pressure Pi 1  at that time. Note that, a phase difference of 180° is present between the crank angle CA of the first cylinder and the crank angle CA of the second cylinder, but the injection-valve fuel pressures at the same reference crank angle (for example, at a compression top dead center) are shown in the graph of  FIG. 4 . 
         [0148]    As understood from  FIG. 4 , the amplitude of the fluctuation indicated by the broken line Ln 2  is reduced as compared to the solid line Lp 2  according to the related-art device. That is, in the first device, the fluctuation of the first injection-valve fuel pressure Pi 1 , which is caused by the fuel injection from the second fuel injection valve  11   b , is suppressed as compared to the related-art device. 
         [0149]    As described above, according to the first device, it is possible to suppress the influence of the fuel pressure fluctuation caused along with the fuel injection from any one of the first fuel injection valve  11   a  to the fourth fuel injection valve  11   d  on the fuel injection from another fuel injection valve connected to the fuel injection valve by the first injection-valve connection pipe  13   a  or the second injection-valve connection pipe  13   b.    
         [0150]    In addition, the characteristics of the fluctuations of the first injection-valve fuel pressure Pi 1  to the fourth injection-valve fuel pressure Pi 4  are similar to each other. Therefore, there is no need to adapt different fuel injection period adjustment maps to the first fuel injection valve  11   a  to the fourth fuel injection valve  11   d , respectively, and hence the ECU  20  only needs to store a single fuel injection period adjustment map. Thus, according to the first device, it is possible to reduce the number of adaptation steps for generating the fuel injection period adjustment map. 
       Second Embodiment 
       [0151]    Next, description is given of a fuel injection device  30  for an internal combustion engine according to a second embodiment of the present invention (hereinafter also referred to as “second device”). The first device is applied to the in-line four-cylinder engine. In contrast, the second device is different from the first device only in that the second device is applied to an in-line six-cylinder engine (hereinafter also referred to simply as “engine”). Thus, the difference is mainly described below. 
         [0152]      FIG. 5  is a schematic illustration of the fuel injection device  30 . The fuel injection device  30  includes a first fuel injection valve  31   a  to a sixth fuel injection valve  31   f,  a first fuel supply pipe  32   a  to a sixth fuel supply pipe  32   f , a first injection-valve connection pipe  33   a  to a third injection-valve connection pipe  33   c,  a common rail  34 , and a first orifice  37   a  to a sixth orifice  37   f.    
         [0153]    Each of the first fuel injection valve  31   a  to the sixth fuel injection valve  31   f  has a configuration similar to that of the fuel injection valve according to the first embodiment (that is, each of the first fuel injection valve  11   a  to the fourth fuel injection valve  11   d ). The first fuel injection valve  31   a  to the sixth fuel injection valve  31   f  are provided to the six cylinders (not shown) (first cylinder to sixth cylinder) of the engine, respectively. The first cylinder to the sixth cylinder are arrayed in line in the stated order. Thus, the first fuel injection valve  31   a  to the sixth fuel injection valve  31   f  are arrayed in line in the stated order. 
         [0154]    The lengths of the first fuel supply pipe  32   a  to the sixth fuel supply pipe  32   f  are equal to each other. The channel sectional areas of the first fuel supply pipe  32   a  to the sixth fuel supply pipe  32   f  are uniform and equal to each other. 
         [0155]    The lengths of the first injection-valve connection pipe  33   a  to the third injection-valve connection pipe  33   c  are equal to each other. The channel sectional areas of the first injection-valve connection pipe  33   a  to the third injection-valve connection pipe  33   c  are uniform and equal to each other. 
         [0156]    The first fuel supply pipe  32   a  connects the common rail  34  and a first supply port  35   a  of the first fuel injection valve  31   a.  The second fuel supply pipe  32   b  connects the common rail  34  and a first supply port  35   b  of the second fuel injection valve  31   b . The third fuel supply pipe  32   c  connects the common rail  34  and a first supply port  35   c  of the third fuel injection valve  31   c.    
         [0157]    The fourth fuel supply pipe  32   d  connects the common rail  34  and a first supply port  35   d  of the fourth fuel injection valve  31   d.  The fifth fuel supply pipe  32   e  connects the common rail  34  and a first supply port  35   e  of the fifth fuel injection valve  31   e.  The sixth fuel supply pipe  32   f  connects the common rail  34  and a first supply port  351  of the sixth fuel injection valve  31   f.    
         [0158]    The first orifice  37   a  to the sixth orifice  37   f  are interposed between the first fuel supply pipe  32   a  to the sixth fuel supply pipe  32   f  and the common rail  34 , respectively. The fuel is fed under pressure from a fuel pump (not shown) to the common rail  34  through a high-pressure pipe  34   a.    
         [0159]    The first injection-valve connection pipe  33   a  connects a second supply port  36   a  of the first fuel injection valve  31   a  and a second supply port  36   f  of the sixth fuel injection valve  31   f . The second injection-valve connection pipe  33   b  connects a second supply port  36   b  of the second fuel injection valve  31   b  and a second supply port  36   e  of the fifth fuel injection valve  31   e.  The third injection-valve connection pipe  33   c  connects a second supply port  36   c  of the third fuel injection valve  31   c  and a second supply port  36   d  of the fourth fuel injection valve  31   d.    
         [0160]    As described above, also in the second device, the channel sectional areas and the lengths of the plurality of fuel supply pipes are equal to each other, and the channel sectional areas and the lengths of the plurality of injection-valve connection pipes are equal to each other. Therefore, the characteristics of fuel pressure fluctuations, which are caused along with the fuel injection from the first fuel injection valve  31   a  to the sixth fuel injection valve  31   f,  are similar to each other. Thus, when further fuel injection (second-stage injection) is performed after the fuel injection (first-stage injection) for the same cycle, an ECU (not shown) of the fuel injection device  30  acquires (predicts) the injection-valve fuel pressure at the start of second-stage injection based on a common fuel injection period adjustment map. In other words, the ECU stores a single fuel injection period adjustment map, but does not store a plurality of fuel injection period adjustment maps corresponding to the first fuel injection valve  31   a  to the sixth fuel injection valve  31   f,  respectively. 
         [0161]    Meanwhile, the ECU of the fuel injection device  30  performs the fuel injection in an order of the first fuel injection valve  31   a,  the fifth fuel injection valve  31   e,  the third fuel injection valve  31   c,  the sixth fuel injection valve  31   f , the second fuel injection valve  31   b,  and the fourth fuel injection valve  31   d . That is, the engine is constructed such that the combustions are performed in an order of the first cylinder, the fifth cylinder, the third cylinder, the sixth cylinder, the second cylinder, and the fourth cylinder. 
         [0162]    In other words, a pair of cylinders to which a pair of fuel injection valves connected by each of the first injection-valve connection pipe  33   a  to the third injection-valve connection pipe  33   c  are provided are non-contiguous in the order of combustions. Thus, a certain length of time is taken since the end of fuel injection from one of the pair of fuel injection valves until the start of fuel injection from the other one of the pair of fuel injection valves. As a result, the fuel pressure fluctuation caused along with the fuel injection from one of the pair of fuel injection valves is mitigated at the start of fuel injection from the other one of the pair of fuel injection valves. 
         [0163]    As described above, according to the second device, there is no need to adapt the plurality of fuel injection period adjustment maps, thereby being capable of reducing the number of adaptation steps for generating the fuel injection period adjustment map. In addition, according to the second device, it is possible to suppress the influence of the fuel pressure fluctuation caused along with the fuel injection from any one of the first fuel injection valve  31   a  to the sixth fuel injection valve  31   f  on the fuel injection from another fuel injection valve connected by any one of the first injection-valve connection pipe  33   a  to the third injection-valve connection pipe  33   c.    
       Third Embodiment 
       [0164]    Next, description is given of a fuel injection device  40  for an internal combustion engine according to a third embodiment of the present invention (hereinafter also referred to as “third device”). In the second device, the first fuel injection valve and the sixth fuel injection valve are connected by the injection-valve connection pipe, the second fuel injection valve and the fifth fuel injection valve are connected by the injection-valve connection pipe, and the third fuel injection valve and the fourth fuel injection valve are connected by the injection-valve connection pipe. 
         [0165]    In contrast, the third device is different from the second device only in that the first fuel injection valve and the third fuel injection valve are connected by the injection-valve connection pipe, the second fuel injection valve and the fifth fuel injection valve are connected by the injection-valve connection pipe, and the fourth fuel injection valve and the sixth fuel injection valve are connected by the injection-valve connection pipe. Thus, the difference is mainly described below. 
         [0166]      FIG. 8  is a schematic illustration of the fuel injection device  40 . The fuel injection device  40  includes the first fuel injection valve  31   a  to the sixth fuel injection valve  31   f,  the first fuel supply pipe  32   a  to the sixth fuel supply pipe  32   f,  a first injection-valve connection pipe  43   a  to a third injection-valve connection pipe  43   c,  the common rail  34 , and the first orifice  37   a  to the sixth orifice  37   f.    
         [0167]    The first injection-valve connection pipe  43   a  connects the second supply port  36   a  of the first fuel injection valve  31   a  and the second supply port  36   c  of the third fuel injection valve  31   c.  The second injection-valve connection pipe  43   b  connects the second supply port  36   b  of the second fuel injection valve  31   b  and the second supply port  36   e  of the fifth fuel injection valve  31   e.  The third injection-valve connection pipe  43   c  connects the second supply port  36   d  of the fourth fuel injection valve  31   d  and the second supply port  36   f  of the sixth fuel injection valve  31   f.    
         [0168]    The lengths of the first fuel supply pipe  32   a  to the sixth fuel supply pipe  32   f  are equal to each other. The channel sectional areas of the first fuel supply pipe  32   a  to the sixth fuel supply pipe  321  are uniform and equal to each other. 
         [0169]    The lengths of the first injection-valve connection pipe  43   a  to the third injection-valve connection pipe  43   c  are equal to each other. The channel sectional areas of the first injection-valve connection pipe  43   a  to the third injection-valve connection pipe  43   c  are uniform and equal to each other. 
         [0170]    Therefore, the characteristics of fuel pressure fluctuations, which are caused along with the fuel injection from the first fuel injection valve  31   a  to the sixth fuel injection valve  31   f,  are similar to each other. Thus, when further fuel injection (second-stage injection) is performed after the fuel injection (first-stage injection) for the same cycle, an ECU (not shown) of the fuel injection device  40  acquires (predicts) the injection-valve fuel pressure at the start of second-stage injection based on a common fuel injection period adjustment map. 
         [0171]    Meanwhile, the ECU of the fuel injection device  40  performs the fuel injection in an order of the first fuel injection valve  31   a,  the fourth fuel injection valve  31   d,  the second fuel injection valve  31   b,  the third fuel Injection valve  31   c,  the sixth fuel injection valve  31   f,  and the fifth fuel injection valve  31   e.  That is, the engine is constructed such that the combustions are performed in an order of the first cylinder, the fourth cylinder, the second cylinder, the third cylinder, the sixth cylinder, and the fifth cylinder. 
         [0172]    In other words, a pair of cylinders to which a pair of fuel injection valves connected by each of the first injection-valve connection pipe  43   a  to the third injection-valve connection pipe  43   c  are provided are non-contiguous in the order of combustions. Thus, a certain length of time is taken since the end of fuel injection from one of the pair of fuel injection valves until the start of fuel injection from the other one of the pair of fuel injection valves. As a result, the fuel pressure fluctuation caused along with the fuel injection from one of the pair of fuel injection valves is mitigated at the start of fuel injection from the other one of the pair of fuel injection valves. 
         [0173]    As described above, according to the third device, there is no need to adapt the plurality of fuel injection period adjustment maps, and hence it is only necessary to store a single common fuel injection period adjustment map. Thus, it is possible to reduce the number of adaptation steps for generating the fuel injection period adjustment map. In addition, according to the third device, it is possible to suppress the influence of the fuel pressure fluctuation caused along with the fuel injection from any one of the first fuel injection valve  31   a  to the sixth fuel injection valve  31   f  on the fuel injection from another fuel injection valve connected by any one of the first injection-valve connection pipe  43   a  to the third injection-valve connection pipe  43   c.    
       Fourth Embodiment 
       [0174]    Next, description is given of a fuel injection device  50  for an internal combustion engine according to a fourth embodiment of the present invention (hereinafter also referred to as “fourth device”). The second device is applied to the in-line six-cylinder engine. In contrast, the fourth device is different from the second device only in that the fourth device is applied to a V-type six-cylinder engine (hereinafter also referred to simply as “engine”). Thus, the difference is mainly described below. 
         [0175]      FIG. 7  is a schematic illustration of the fuel injection device  50 . The fuel injection device  50  includes a first fuel injection valve  51   a  to a sixth fuel injection valve  51   f,  a first fuel supply pipe  52   a  to a sixth fuel supply pipe  52   f , a first injection-valve connection pipe  53   a  to a third injection-valve connection pipe  53   c,  a first common rail  54   a,  a second common rail  54   b,  and a first orifice  57   a  to a sixth orifice  57   f.    
         [0176]    Each of the first fuel injection valve  51   a  to the sixth fuel injection valve  51   f  has a configuration similar to that of the fuel injection valve according to the first embodiment (that is, each of the first fuel injection valve  11   a  to the fourth fuel injection valve  11   d ). The first fuel injection valve  51   a  to the sixth fuel injection valve  51   f  are provided to the six cylinders (not shown) (first cylinder to sixth cylinder) of the engine, respectively. 
         [0177]    A first bank (first cylinder group) of the engine is constructed of the first cylinder, the third cylinder, and the fifth cylinder, whereas a second bank (second cylinder group) of the engine is constructed of the second cylinder, the fourth cylinder, and the sixth cylinder. The first bank and the second bank are opposed to each other at a predetermined bank angle. 
         [0178]    The first cylinder, the third cylinder, and the fifth cylinder are arrayed in line in the stated order, and hence the first fuel injection valve  51   a,  the third fuel injection valve  51   c,  and the fifth fuel injection valve  51   e  are arrayed in line in the stated order. Meanwhile, the second cylinder, the fourth cylinder, and the sixth cylinder are arrayed in line in the stated order, and hence the second fuel injection valve  51   b,  the fourth fuel injection valve  51   d,  and the sixth fuel injection valve  51   f  are arrayed in line in the stated order. 
         [0179]    The first fuel supply pipe  52   a  connects the first common rail  54   a  and a first supply port  55   a  of the first fuel injection valve  51   a.  The second fuel supply pipe  52   b  connects the second common rail  54   b  and a first supply port  55   b  of the second fuel injection valve  51   b.  The third fuel supply pipe  52   c  connects the first common rail  54   a  and a first supply port  55   c  of the third fuel injection valve  51   c.    
         [0180]    The fourth fuel supply pipe  52   d  connects the second common rail  54   b  and a first supply port  55   d  of the fourth fuel injection valve  51   d.  The fifth fuel supply pipe  52   e  connects the first common rail  54   a  and a first supply port  55   e  of the fifth fuel injection valve  51   e.  The sixth fuel supply pipe  52   f  connects the second common rail  54   b  and a first supply port  55   f  of the sixth fuel injection valve  51   f.    
         [0181]    The first orifice  57   a,  the third orifice  57   c,  and the fifth orifice  57   e  are interposed between the first fuel supply pipe  52   a,  the third fuel supply pipe  52   c,  and the fifth fuel supply pipe  52   e  and the first common rail  54   a , respectively. The second orifice  57   b,  the fourth orifice  57   d,  and the sixth orifice  57   f  are interposed between the second fuel supply pipe  52   b,  the fourth fuel supply pipe  52   d,  and the sixth fuel supply pipe  52   f  and the second common rail  54   b,  respectively. 
         [0182]    The fuel is fed under pressure from a fuel pump (not shown) to the first common rail  54   a  through a high-pressure pipe  58   a.  The fuel is fed under pressure from the fuel pump to the second common rail  54   b  through a high-pressure pipe  58   b.    
         [0183]    The first injection-valve connection pipe  53   a  connects a second supply port  56   a  of the first fuel injection valve  51   a  and a second supply port  56   d  of the fourth fuel injection valve  51   d.  The second injection-valve connection pipe  53   b  connects a second supply port  56   b  of the second fuel injection valve  51   b  and a second supply port  56   e  of the fifth fuel injection valve  51   e.  The third injection-valve connection pipe  53   c  connects a second supply port  56   c  of the third fuel injection valve  51   c  and a second supply port  56   f  of the sixth fuel injection valve  51   f.    
         [0184]    The lengths of the first fuel supply pipe  52   a  to the sixth fuel supply pipe  52   f  are equal to each other. The channel sectional areas of the first fuel supply pipe  52   a  to the sixth fuel supply pipe  52   f  are uniform and equal to each other. 
         [0185]    The lengths of the first injection-valve connection pipe  53   a  to the third injection-valve connection pipe  53   c  are equal to each other. The channel sectional areas of the first injection-valve connection pipe  53   a  to the third injection-valve connection pipe  53   c  are uniform and equal to each other. 
         [0186]    Therefore, the characteristics of fuel pressure fluctuations, which are caused along with the fuel injection from the first fuel injection valve  51   a  to the sixth fuel injection valve  51   f,  are similar to each other. Thus, when further fuel injection (second-stage injection) is performed after the fuel injection (first-stage injection) for the same cycle, an ECU (not shown) of the fuel injection device  50  acquires (predicts) the injection-valve fuel pressure at the start of second-stage injection based on a common fuel injection period adjustment map. 
         [0187]    Meanwhile, the ECU of the fuel injection device  50  performs the fuel injection in an order of the first fuel injection valve  51   a,  the second fuel injection valve  51   b,  the third fuel injection valve  51   c,  the fourth fuel injection valve  51   d,  the fifth fuel injection valve  51   e,  and the sixth fuel injection valve  51   f.  That is, the engine is constructed such that the combustions are performed in an order of the first cylinder, the second cylinder, the third cylinder, the fourth cylinder, the fifth cylinder, and the sixth cylinder. 
         [0188]    In other words, a pair of cylinders to which a pair of fuel injection valves connected by each of the first injection-valve connection pipe  53   a  to the third injection-valve connection pipe  53   c  are provided are non-contiguous in the order of combustions. Thus, a certain length of time is taken since the end of fuel injection from one of the pair of fuel injection valves until the start of fuel injection from the other one of the pair of fuel injection valves. As a result, the fuel pressure fluctuation caused along with the fuel injection from one of the pair of fuel injection valves is mitigated at the start of fuel injection from the other one of the pair of fuel injection valves. 
         [0189]    As described above, according to the fourth device, there is no need to adapt the plurality of fuel injection period adjustment maps, and hence it is only necessary to store a single common fuel injection period adjustment map. Thus, it is possible to reduce the number of adaptation steps for generating the fuel injection period adjustment map. In addition, according to the fourth device, it is possible to suppress the influence of the fuel pressure fluctuation caused along with the fuel injection from any one of the first fuel injection valve  51   a  to the sixth fuel injection valve  51   f  on the fuel injection from another fuel injection valve connected by any one of the first injection-valve connection pipe  53   a  to the third injection-valve connection pipe  53   c.    
       Fifth Embodiment 
       [0190]    Next, description is given of a fuel injection device  60  for an internal combustion engine according to a fifth embodiment of the present invention (hereinafter also referred to as “fifth device”). In the fourth device, the first fuel injection valve and the fourth fuel injection valve are connected by the injection-valve connection pipe, the second fuel injection valve and the fifth fuel injection valve are connected by the injection-valve connection pipe, and the third fuel injection valve and the sixth fuel injection valve are connected by the injection-valve connection pipe. 
         [0191]    In contrast, the fifth device is different from the fourth device only in that the first fuel injection valve and the third fuel injection valve are connected by the injection-valve connection pipe, the second fuel injection valve and the fifth fuel injection valve are connected by the injection-valve connection pipe, and the fourth fuel injection valve and the sixth fuel injection valve are connected by the injection-valve connection pipe. Thus, the difference is mainly described. 
         [0192]      FIG. 8  is a schematic illustration of the fuel injection device  60 . The fuel injection device  60  includes the first fuel injection valve  51   a  to the sixth fuel injection valve  51   f,  the first fuel supply pipe  52   a  to the sixth fuel supply pipe  52   f,  a first injection-valve connection pipe  63   a  to a third injection-valve connection pipe  63   c,  the first common rail  54   a,  the second common rail  54   b , and the first orifice  57   a  to the sixth orifice  57   f.    
         [0193]    The first injection-valve connection pipe  63   a  connects the second supply port  56   a  of the first fuel injection valve  51   a  and the second supply port  56   c  of the third fuel injection valve  51   c.  The second injection-valve connection pipe  63   b  connects the second supply port  56   b  of the second fuel injection valve  51   b  and the second supply port  56   e  of the fifth fuel injection valve  51   e.  The third injection-valve connection pipe  63   c  connects the second supply port  56   d  of the fourth fuel injection valve  51   d  and the second supply port  56   f  of the sixth fuel injection valve  51   f.    
         [0194]    The lengths of the first fuel supply pipe  52   a  to the sixth fuel supply pipe  52   f  are equal to each other. The channel sectional areas of the first fuel supply pipe  52   a  to the sixth fuel supply pipe  52   f  are uniform and equal to each other. 
         [0195]    The lengths of the first injection-valve connection pipe  63   a  to the third injection-valve connection pipe  63   c  are equal to each other. The channel sectional areas of the first injection-valve connection pipe  63   a  to the third injection-valve connection pipe  63   c  are uniform and equal to each other, 
         [0196]    Therefore, the characteristics of fuel pressure fluctuations, which are caused along with the fuel injection from the first fuel injection valve  51   a  to the sixth fuel injection valve  51   f,  are similar to each other. Thus, when further fuel injection (second-stage injection) is performed after the fuel injection (first-stage injection) for the same cycle, an ECU (not shown) of the fuel injection device  60  acquires (predicts) the injection-valve fuel pressure at the start of second-stage injection based on a common fuel injection period adjustment map. 
         [0197]    Meanwhile, the ECU of the fuel injection device  60  performs the fuel injection in an order of the first fuel injection valve  51   a,  the second fuel injection valve  51   b,  the third fuel injection valve  51   c,  the fourth fuel injection valve  51   d,  the fifth fuel injection valve  51   e,  and the sixth fuel injection valve  51   f.  That is, the engine is constructed such that the combustions are performed in an order of the first cylinder, the second cylinder, the third cylinder, the fourth cylinder, the fifth cylinder, and the sixth cylinder. 
         [0198]    In other words, a pair of cylinders to which a pair of fuel injection valves connected by each of the first injection-valve connection pipe  63   a  to the third injection-valve connection pipe  63   c  are provided are non-contiguous in the order of combustions. Thus, a certain length of time is taken since the end of fuel injection from one of the pair of fuel injection valves until the start of fuel injection from the other one of the pair of fuel injection valves. As a result, the fuel pressure fluctuation caused along with the fuel injection from one of the pair of fuel injection valves is mitigated at the start of fuel injection from the other one of the pair of fuel injection valves. 
         [0199]    As described above, according to the fifth device, there is no need to adapt the plurality of fuel injection period adjustment maps, and hence it is only necessary to store a single common fuel injection period adjustment map. Thus, it is possible to reduce the number of adaptation steps for generating the fuel injection period adjustment map. In addition, according to the fifth device, it is possible to suppress the influence of the fuel pressure fluctuation caused along with the fuel injection from any one of the first fuel injection valve  51   a  to the sixth fuel injection valve  51   f  on the fuel injection from another fuel injection valve connected by any one of the first injection-valve connection pipe  63   a  to the third injection-valve connection pipe  63   c.    
         [0200]    In the above, the fuel injection device for an internal combustion engine according to each of the embodiments of the present invention is described, but the present invention is not limited to the above-mentioned embodiments, and various modifications may be made without departing from the object of the present invention. For example, the fuel injection device according to each of the embodiments is applied to the in-line four-cylinder engine, the in-line six-cylinder engine, or the V-type six-cylinder engine. However, the fuel injection device may be applied to an engine with an even number of cylinders including eight or more cylinders. Alternatively, the fuel injection device may be applied to a horizontally-opposed engine (for example, a horizontally-opposed six-cylinder engine). 
         [0201]    In addition, the fuel injection device according to each of the embodiments includes the fuel supply pipes and the injection-valve connection pipes having uniform channel sectional areas. However, the fuel supply pipes and/or the injection-valve connection pipes may have non-uniform channel sectional areas. When the channel sectional areas of the fuel supply pipes are not uniform, the fuel supply pipes are constructed such that the channel sectional areas of portions equidistant from the ends on one side (for example, the ends on the first supply port side) become equal to each other. When the channel sectional areas of the injection-valve connection pipes are not uniform, the injection-valve connection pipes are constructed such that the channel sectional areas of portions equidistant from the ends on one side become equal to each other.