Abstract:
A valve actuating device is provided which may be employed in fuel injectors for automotive internal combustion engines. The valve actuating device includes an actuator, a large-diameter piston displaced by said actuator, a small-diameter piston operating a valve, a displacement amplifying chamber filled with working fluid to amplify and transmit displacement of the large-diameter piston to the small-diameter piston, and a drain passage. The drain passage communicates with the displacement amplifying chamber through a pinhole for draining the working fluid within the displacement amplifying chamber, thereby enabling the pressure in the displacement amplifying chamber to be released in order to ensure the movement of the small-diameter piston when the valve actuating device is started.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field of the Invention  
           [0002]    The present invention relates generally to a valve actuating device equipped with an electrically operated actuator and a fuel injector for internal combustion engines equipped with such a valve actuating device.  
           [0003]    2. Background Art  
           [0004]    Hydraulic fuel injectors equipped with a piezoelectric valve actuator are used in internal combustion diesel engines of automotive vehicles. Such a fuel injector includes a large-diameter piston moved by the expansion and contraction of the piezoelectric valve actuator, a pressure chamber filled with hydraulic fluid, and a small-diameter piston which are arranged in alignment with each other. The movement of the large-diameter piston causes the hydraulic fluid in the pressure chamber to change in pressure, which moves the small-diameter piston. The small-diameter piston then actuates a control valve.  
           [0005]    When it is required to emit a fuel spray, the piezoelectric valve actuator is energized so that it expands to increase the hydraulic pressure in the pressure chamber through the large-diameter piston. This causes the expansion of the piezoelectric valve actuator to be amplified hydraulically and transmitted to the small-diameter piston. The small-diameter piston then moves downward and opens the control valve. When the control valve is opened, it will cause the pressure in a back pressure chamber to drop, thereby lifting up a nozzle needle to initiate fuel injection. Contracting the piezoelectric valve actuator will cause the small-diameter piston to move upward, thereby closing the control valve to terminate the fuel injection.  
           [0006]    There is known the above type of fuel injector which has disposed therein a hydraulic mechanism designed to supply working fluid to the pressure chamber through a check valve in order to compensate for a leakage of working fluid from the pressure chamber. For example, U.S. Pat. No. 5,779,149 to Hayes, Jr. teaches a fuel injector which has formed therein a fluid passage serving to direct the fuel leaking from a nozzle needle to a pressure chamber through a check valve made up of a ball valve and a coil spring. U.S. Pat. No. 6,155,532 (corresponding to Japanese Patent First Publication No. 11-166653) teaches a fuel injector which has a refill valve disposed in a radial direction of a pressure chamber for compensating for a leakage of fuel from the pressure chamber. The refill valve is, like the above structure, made up of a ball valve and a coil spring.  
           [0007]    The above structures, however, have three drawbacks as discussed below.  
           [0008]    (1) The pressure chamber being filled with the working fluid after assembly of the fuel injector, air may be left in the pressure chamber, thus resulting in instability of operation of the fuel injector. (2) The small-diameter piston falls downward by the gravity while the fuel injector is at rest for a long period of time, so that an amount of working fluid equivalent to a change in volume of the pressure chamber is supplied to the pressure chamber through the check valve, thereby making it difficult to lift up the small-diameter piston, which disenables a subsequent operation of the fuel injector. (3) If power supply to the piezoelectric valve actuator is cut undesirably during expansion of the piezoelectric valve actuator, it becomes impossible for the piezoelectric valve actuator to contract, thus resulting in the pressure in the pressure chamber being kept at higher levels, which causes the fuel to continue to be sprayed from the fuel injector. Further improvement of controllability and safety of fuel injectors is, therefore, sought.  
         SUMMARY OF THE INVENTION  
         [0009]    It is therefore a principal object of the invention to avoid the disadvantages of the prior art.  
           [0010]    It is another object of the invention to provide an improved structure of a valve actuating device which assures higher controllability and safety in operation and a fuel injector equipped with such a valve actuating device.  
           [0011]    According to one aspect of the invention, there is provided a valve actuating device which may be used in a fuel injector for automotive internal combustion engines. The valve actuating device comprises: (a) an actuator; (b) a first piston displaced by the actuator; (c) a second piston operating a valve, the second piston being smaller in diameter than the first piston; (d) a displacement amplifying chamber provided between the first piston and the second piston, the displacement amplifying chamber being filled with working fluid to amplify and transmit displacement of the first piston to the second piston; and (e) a drain passage communicating with the displacement amplifying chamber through a pinhole for draining the working fluid within the displacement amplifying chamber.  
           [0012]    In the preferred mode of the invention, the diameter of the pinhole is within 0.02 to 0.5 mm.  
           [0013]    A check valve is disposed between the displacement amplifying chamber and the drain passage which allows the working fluid to flow only from the drain passage to the displacement amplifying chamber. The check valve includes a flat valve in which the pinhole is formed.  
           [0014]    The first piston has formed therein a passage leading to the drain passage. The pinhole is provided between the passage and the displacement amplifying chamber.  
           [0015]    The first piston has a length in which the passage extends longitudinally and has an opening formed in a first end of the length exposed to the displacement amplifying chamber. The flat valve of the check valve is disposed on the opening of the passage to allow the working fluid to flow only from the drain passage to the displacement amplifying chamber through the passage. The pinhole is formed in the flat valve of the check valve.  
           [0016]    An oil sump is formed on a side of a second end of the first piston opposite the first end and establishes fluid communication between the drain passage and the passage.  
           [0017]    A spring chamber is formed on the side of the first end of the first piston in which a spring is disposed to urge the actuator away from the displacement amplifying chamber. The spring chamber defines the oil sump.  
           [0018]    According to another aspect of the invention, there is provided a fuel injector which may be employed in automotive internal combustion engines. The fuel injector comprises: (a) an injector body; (b) a fuel inlet passage formed in the injector body; (c) an actuator; (d) a first piston displaced by the actuator; (e) a second piston smaller in diameter than the first piston, the second piston operating a valve for spraying fuel supplied from the fuel inlet passage from a spray hole; (f) a displacement amplifying chamber formed between the first piston and the second piston within the injector body, the displacement amplifying chamber being filled with working fluid to amplify and transmit displacement of the first piston to the second piston; and (g) a drain passage formed in the injector body which communicates with the displacement amplifying chamber through a pinhole for draining the working fluid within the displacement amplifying chamber.  
           [0019]    In the preferred mode of the invention, the displacement amplifying chamber is filled with the working fluid at a factory.  
           [0020]    The working fluid is injected into the displacement amplifying chamber at the factory after the displacement amplifying chamber is evacuated.  
           [0021]    The injector body is sealed to avoid leaking of the working fluid in the displacement amplifying chamber out of the injector body. 
       
    
    
     BRIEF DESPCRIPTION OF THE DRAWINGS  
       [0022]    The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.  
         [0023]    In the drawings:  
         [0024]    [0024]FIG. 1 is a vertical sectional view which shows a fuel injector equipped with a valve actuating device according to the first embodiment of the invention;  
         [0025]    [0025]FIG. 2( a ) is a sectional view which shows a flat valve of a check valve installed in the fuel injector of FIG. 1;  
         [0026]    [0026]FIG. 2( b ) is a plan view of FIG. 2( a );  
         [0027]    [0027]FIG. 2( c ) is a perspective view which shows a conical spring of a check valve;  
         [0028]    [0028]FIG. 3( a ) is a time chart which shows the voltage applied to a piezoelectric actuator;  
         [0029]    [0029]FIG. 3( b ) is a time chart which shows the pressure in a displacement amplifying chamber;  
         [0030]    [0030]FIG. 3( c ) is a time charts which shows the amount of lift of a ball valve used to control the pressure in a control chamber;  
         [0031]    [0031]FIG. 3( d ) is a time chart which shows the pressure in a control chamber;  
         [0032]    [0032]FIG. 3( e ) is a time chart which shows the amount of lift of a nozzle needle;  
         [0033]    [0033]FIG. 4( a ) is a sectional view which shows a spring which may be used instead of the conical spring of FIG. 2( c ); and  
         [0034]    [0034]FIG. 4( b ) is a plan view of FIG. 4( a ). 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    Referring to the drawings, wherein like reference numbers refer to like parts in several views, particularly to FIG. 1, there is shown a fuel injector  100  according to the invention. The following discussion will refer to, as an example, a common rail fuel injection system in which the fuel injector  100  is provided for each cylinder of a diesel engine. The common rail fuel injection system includes a common rail which accumulates therein fuel supplied from a fuel tank elevated in pressure by a fuel pump installed on the engine. When it is required to inject the fuel into the engine, the fuel stored in the common rail is supplied to the fuel injectors  100  under high pressure.  
         [0036]    The fuel injector  100  is designed to move a nozzle needle  12  vertically to open or close a spray hole  11  formed in a head of a nozzle body B 1  for initiating or terminating fuel injection. The spray hole  11  is opened upon movement of the nozzle needle  12  to an upper limit position and communicates with a fuel sump  31  leading to a high-pressure passage  3 , so that the fuel is supplied to the spray hole  11 . The spray hole  11  is closed upon movement of the nozzle needle  12  to a lower limit position, so that the communication with the fuel sump  31  is blocked to cut the fuel supply to the spray hole  11 . The low limit position of the nozzle needle  12  is defined by a nozzle seat  13  on which the nozzle needle  12  is seated. The upper limit position is defined by an orifice plate P 1  disposed above the nozzle body B 1 .  
         [0037]    The nozzle body B 1  is installed on a lower end of a housing H of a valve actuating device  1  through orifice plates P 1  and P 2  and disposed within a nozzle holder B 2  in liquid-tight form. The high-pressure passage  3  extends upward from the fuel sump  31  to the common rail through the orifice plates P 1  and P 2  and the housing H. Within the housing H, a drain passage  2  is formed which leads to the fuel tank. A control chamber  4  is defined between an upper end of the nozzle needle  12  and the orifice plate P 1 . The nozzle needle  12  is urged downward, as viewed in the drawing, by the spring pressure of a coil spring  41  and the hydraulic pressure within the control chamber  4  to close the spray hole  11  at all times.  
         [0038]    The hydraulic pressure in the control chamber  4  is controlled by the activity of a three-way valve  5  of the valve actuating device  1 . The three-way valve  5  consists of a conical valve chamber  51  formed in a lower end of the housing H and a ball valve  52 . The valve chamber  51  always communicates with the control chamber  4  through a passage extending through the orifice plates P 1  and P 2  and a main orifice  42  formed in the passage. The valve chamber  51  has two ports: a drain port  21  and a high-pressure port  32 . The ball valve  52  closes either the drain port  21  or the high-pressure port  32  at all times, thereby establishing fluid communication between one of the drain port  21  and the high-pressure port  32  and the control chamber  4 . The drain port  21  communicates with the drain passage  2  through a spill chamber  22  formed above the valve chamber  51 . The high-pressure port  32  extends vertically through the orifice plates P 1  and P 2  and communicates with the high-pressure passage  3  through a groove  33  formed in a lower end surface of the orifice plate P 2 .  
         [0039]    Specifically, when the valve chamber  51  communicates with the drain port  21 , it will cause the control chamber  4  to be decreased in pressure, thereby moving the nozzle needle  12  out of the nozzle seat  13 . Alternatively, when the valve chamber  51  communicates with the high-pressure port  32 , it will cause the control chamber to be increased in pressure, thereby moving the nozzle needle  12  downward into engagement with the nozzle seat  13 . The control chamber  4  communicates directly with the high-pressure passage  3  at all times through a sub-orifice  43  formed in the orifice plate P 1 . The sub-orifice  43  serves to supply the fuel from the high-pressure passage  3  to the control chamber  4  to reduce a pressure drop in the control chamber  4  at the start of fuel injection for smoothing the movement of the nozzle needle  12 , while it works to promote a pressure rise in the control chamber  4  to speed up the movement of the nozzle needle  12  when closing the spray hole  11 .  
         [0040]    Around an opening of the drain part  21  leading to the valve chamber  51 , a conical drain seat  53  is formed. Around the high-pressure port  32  leading to the valve chamber  51 , a flat high-pressure seat  54  is formed. The drain seat  53  may alternatively be formed to be flat, while the high-pressure seat  54  may be formed to be conical. This compensates for a lateral shift of the ball valve  52 . The pressure in the valve chamber  51  is always higher than the pressure in the drain port  21 , so that the ball valve  52  is kept seated on the drain seat  53 . The pressure acting on the ball valve  52  to urge it into engagement with the high-pressure seat  54  is provided by a small-diameter piston  18  of the valve actuating device  1 .  
         [0041]    The valve actuating device  1  includes a piezoelectric actuator  14 , an actuator piston  15 , a large-diameter piston  17 , and the small-diameter piston  18 . The piezoelectric actuator  14  is installed in an upper portion of the housing H. The actuator piston  15  is arranged to be movable in contact with a lower end of the piezoelectric actuator  14 . The large-diameter piston  17  connects with the actuator piston  15  through a rod  16 . The small-diameter piston  18  is moved by the large-diameter piston  17  through a displacement amplifying chamber  6 . The piezoelectric actuator  14  is made of a laminated piezoelectric device (also called a piezo stack) which works to expand when electrically charged and contract when discharged. The structure of the piezoelectric device is well known in the art, and explanation thereof in detail will be omitted here. The actuator piston  15  is installed slidably within an actuator cylinder H 1  and connects with the large-diameter piston  17  through the rod  16 . The large-diameter piston  17  and the small-diameter piston  18  are disposed slidably within a large-diameter cylindrical chamber H 3  and a small-diameter cylindrical chamber H 4  formed coaxially within a hollow cylinder H 2 . The rod  16  extends from an upper end surface of the large-diameter piston  17  upwards and is fitted within a lower end surface of the actuator piston  15 .  
         [0042]    Defined below the lower end of the actuator piston  15  around the rod  16  is an oil sump  7  leading to the drain passage  2 . A coil spring  71  is disposed within the oil sump  7  to urge the actuator piston  15  upward together with the large-diameter piston  17 . Specifically, the actuator piston  15  and the large-diameter piston  17  are urged upward by the spring  71 , so that they may move following the expansion or contraction of the piezoelectric actuator  14 . An O-ring  73  is installed in an annular groove formed in a side wall of the actuator piston  15  for protecting the piezoelectric actuator  14  from contamination of working fluid (i.e., the fuel) within the oil sump  7 . The oils sump  7  communicates with the drain passage  2  through a passage  95 . The passage  95  is formed by drilling side walls of the housing Hand the actuator cylinder H 1  and closing a hole formed the housing H using a plug  74 .  
         [0043]    The hollow cylinder H 2  has formed on an inner wall between the small-diameter cylinder chamber H 4  and the large-diameter cylinder chamber H 3  an inner shoulder working as a stopper  61  which defines an upper limit of the small-diameter piston  18 . The small-diameter cylinder chamber H 4  and the large-diameter cylinder chamber H 3  communicate with each other through a central hole formed in the stopper  61 . The small-diameter cylinder chamber H 4  defines a hydraulic chamber A between the upper end thereof and the stopper  61 . The large-diameter cylinder chamber H 3  defines a hydraulic chamber B between the lower end thereof and the stopper  61 . The hydraulic chambers A and B define the displacement amplifying chamber  6 . The displacement amplifying chamber  6  works to transmit the longitudinal displacement of the large-diameter piston  17  to the small-diameter piston  18 . Specifically, the stroke of the large-diameter piston  17  (i.e., the vertical movement of the piezoelectric actuator  14 ) is amplified through the fuel within the displacement amplifying chamber  6  as a function of a difference in diameter between the large-diameter piston  17  and the small-diameter piston  18  (e.g., two or three times the displacement of the large-diameter piston  17 ) and transmitted to the small-diameter piston  18 . A lower portion of the small-diameter piston  18  lies within the spill chamber  22 . The small-diameter piston  18  has a thin head which extends into the drain port  21  and contacts with the ball valve  52 .  
         [0044]    Within the large-diameter piston  18 , a vertical passage  72  extends and communicates at an upper end thereof with a lateral passage opening into the oil sump  7 . The vertical passage  72  extends at a lower end thereof to the lower end of the large-diameter piston  17  and communicates with the displacement amplifying chamber  6  through a check valve  8  installed on the lower end of the large-diameter piston  17 . The check valve  8  works to compensate for a loss of fuel caused by leakage from the oil sump  7  to the displacement amplifying chamber  6  and consists of a flat valve  81  closing the lower opening of the passage  72  and a conical spring  82  urging the flat valve  81  upwards. The flat valve  81  is, as shown in FIGS.  2 ( a ) and  2 ( b ), made of a thin disc which has a thickness of 0.1 to 0.2 mm and parallel sides  86 . A pinhole  84  is formed in the center of the flat valve  81  which has a diameter of 0.02 to 0.5 mm.  
         [0045]    The conical spring  82  is, as shown in FIG. 2( c ), made of an annular plate having a thickness of 0.01 to 005 mm and shaped to produce a pressure of 0.5 to 2N. The flat valve  81  and the conical spring  82  are disposed within a holder  83  made of a cup-shaped cylinder. The holder  83  is fitted on a lower end portion of the large-diameter piston  18 . A drop in pressure in the displacement amplifying chamber  6  arising from the leakage of fuel will cause the flat valve  81  to move downward against the pressure produced by the conical spring  82 , so that the fuel flows from the passage  72 . The holder  83  has formed in the bottom thereof a hole  85  which is much greater than the pinhole  84  and establishes communication between an inner chamber of the holder  83  and the displacement amplifying chamber  6  for facilitating the flow of fuel into the displacement amplifying chamber  6 .  
         [0046]    In operation of the fuel injector  100 , when it is required to initiate the fuel injection, a voltage of about 100 to 150V is, as indicated as a piezo-voltage in FIG. 3( a ), applied to the piezoelectric actuator  14 . The piezoelectric actuator  14  expands, for example, 40 μm proportional to the applied voltage to move the large-diameter piston  17  downward, thereby elevating, as shown in FIG. 3( b ), the pressure in the displacement amplifying chamber  6  (time t 1  to t 2 ). The pressure in the displacement amplifying chamber  6  leaks into the drain passage  2  through the pinhole  84  of the flat valve  81  and gaps between an outer wall of the large-diameter piston  17  and an inner wall of the hollow cylinder H 2  and between an outer wall of the small-diameter piston  18  and the inner wall of the hollow cylinder H 2 , so that it drops slowly after time t 2 . The elevation in pressure in the displacement amplifying chamber  6  causes the small-diameter piston  18  to move downward to push the ball valve  52  out of engagement with the drain seat  53 , as shown in FIG. 3( c ). The ball valve  52  then rests on the high-pressure seat  54  (time t 2 ). The degree of movement of the ball valve  52  is a multiple of (e.g., two times) the degree of expansion of the piezoelectric actuator  14  which corresponds to a sectional area ratio of the large-diameter piston  17  to the small-diameter piston  18 .  
         [0047]    When the ball valve  52  moves out of engagement with the drain seat  53 , it establishes communication between the valve chamber  51  and the drain port  21 , while it blocks communication between the high-pressure port  32  and the valve chamber  51 , so that the pressure in the valve chamber  51  drops, thereby decreasing, as shown in FIG. 3( d ), the pressure in the control chamber  4 . When the pressure in the fuel sump  31  exceeds the sum of the pressure in the control chamber  4  and the pressure produced by the coil spring  41 , it will cause the nozzle needle  12  to be lifted upwards, as shown in FIG. 3( e ), to open the spray hole  11 , thereby initiating the fuel injection.  
         [0048]    When it is required to terminate the fuel injection, no voltage is applied to the piezoelectric actuator  14  to discharge it electrically (time t 3  to t 5 ). The piezoelectric actuator  14  contracts to an original length thereof, thereby causing the actuator piston  15  to be lifted up by the spring  71 . The large-diameter piston  17  is also lifted up, thus resulting in a decrease in pressure of the displacement amplifying chamber  6 , as shown in FIG. 3( b ). The drop in pressure in the displacement amplifying chamber  6  causes the small-diameter piston  18  to be moved upward together with the ball valve  52  (time t 4 ).  
         [0049]    When the ball valve  52  rests on the drain seat  53  again, it establishes the communication between the valve chamber  51  and the high-pressure port  32 , while blocking the communication between the valve chamber  51  and the drain port  21 , so that the pressure in the valve chamber  51  and the control chamber  4 , as shown in FIG. 3( d ), is returned to the original level. When the pressure in the control chamber  4  rises, and the pressure urging the nozzle needle  12  downward exceeds the pressure in the fuel sump  31 , it will cause the nozzle needle  12  to move downward so that it rests on the nozzle seat  13  again to close the spray hole  11 , thereby terminating the fuel injection (time t 5 ). After time t 5 , the pressure in the displacement amplifying chamber  6  is undershot temporarily by an amount equivalent to a leakage of the fuel during the fuel injection, but the fuel in the oil sump  7  flows into the displacement amplifying chamber  6  through the check valve  8 , so that the pressure in the displacement amplifying chamber  6  is, as shown in FIG. 3( b ), returned quickly to the original level.  
         [0050]    In FIGS.  3 ( a ) to  3 ( e ), dotted lines represent a case where wire connecting an actuator driver and the piezoelectric actuator  14  is broken during the fuel injection. Two-dot chain lines represent a case where the pinhole  84  is not formed in the flat valve  81  of the check valve  8  in such an event.  
         [0051]    If the wire connecting the actuator driver and the piezoelectric actuator  14  is broken during application of voltage to the piezoelectric actuator  14 , it becomes impossible to discharge the piezoelectric actuator  14 , so that the piezo-voltage is kept at a high level, as indicated by the dotted line in FIG. 3( a ). The displacement or expansion of the piezoelectric actuator  14  is held as it is, thus making it impossible to move the actuator piston  15  and the large-diameter piston  17 . In the absence of the pinhole  84 , it becomes impossible to change the pressure in the displacement amplifying chamber  6 . Specifically, a drop in pressure of the displacement amplifying chamber  6  arises only from leakage of fuel from gaps between the outer walls of the large-diameter piston  17  and the small-diameter piston  18  and the inner wall of the hollow cylinder H 2  and continues only for several tens of microseconds (ms). The pressure in the displacement amplifying chamber  6 , thus, hardly decreases, as indicated by the two-dot chain line in FIG. 3( b ), so that the movement of the ball valve  52 , the pressure in the control chamber  4 , and the movement of the nozzle needle  12  hardly change, which may cause the fuel injection to continue.  
         [0052]    In the case where the pinhole  84  is formed in the flat valve  81  of the check valve  8 , the piezo-voltage is kept at a high level, but the fuel in the displacement amplifying chamber  6  leaks into the oil sump  7  through the pinhole  84 , so that the pressure in the displacement amplifying chamber  6 , as indicated by the dotted line in FIG. 3( b ), drops gradually. 3 to 5 ms after the application of voltage to the piezoelectric actuator  14 , the pressure in the displacement amplifying chamber  6  decreases below the pressure in the high-pressure port  32  urging the ball valve  52  upwards, so that the ball valve  52  and the small-diameter piston  18  are lifted upwards together. When the ball valve  52  is seated on the drain seat  53 , it blocks the communication between the drain port  21  and the valve chamber  51 , so that the pressure in the control chamber  4  is, as indicated by the dotted line in FIG. 3( d ), elevated. This causes the nozzle needle  12  to be seated, as indicated by the dotted line in FIG. 3( e ), on the nozzle seat  13  to close the spray hole  11  or terminate the fuel injection.  
         [0053]    In the above event, the quantity of fuel that is some multiple or several tens of multiples of normal is supplied to the internal combustion engine. Usually, the fusion of the engine or failure in engine operation occurs when the quantity of fuel that is some multiple of normal is supplied for several revolutions of the engine. Therefore, the fuel injection only for 3 to 5 ms will not be objectionable in the engine operation. It is advisable that the size of the pinhole  84  be selected so that the fuel injection does not continue over a time required for one revolution of the engine running at a maximum speed. For example, when the engine is running at 5000 rpm, the time required for one revolution of the engine is 24 ms. In this case, the size or diameter of the pinhole  84  is preferably set to within a range of 0.02 to 0.2 mm. If the fuel injection is stopped within 24 ms, most of the fuel is discharged to an exhaust pipe of the engine. However, in order to avoid the deterioration of the catalyst, it is advisable that the size of the pinhole  84  be selected so that the fuel injection does not continue over 3 to 5 ms. This may be achieved by setting the size of the pinhole  84  to 0.05 to 0.5 mm.  
         [0054]    The pinhole  84  also produces the following effects.  
         [0055]    If the displacement amplifying chamber  6  is not filled with the fuel after assembly of the fuel injector  100 , it will cause the displacement of the piezoelectric actuator  6  not to be transmitted to the small-diameter piston effectively. Therefore, if the fuel injector  100  is installed in the engine as it is, the displacement amplifying chamber  6  does not work properly until it is filled with the fuel, thus giving rise to a problem that much time is required to start the engine. Such a problem is eliminated by filling the displacement amplifying chamber  6  with fuel before the fuel injector  100  is shipped or installed in the engine. This may be accomplished by connecting a vacuum pump to the high-pressure passage  3  to evacuate the inside of the fuel injector  100  and supply the fuel from the drain passage  2 . In the absence of the pinhole  84 , it is difficult to evacuate the displacement amplifying chamber  6 , so that air is left in the displacement amplifying chamber  6  after the fuel is injected into the displacement amplifying chamber  6 , which will impinge upon the transmission of the displacement of the piezoelectric actuator  14  to the small-diameter piston  18  adversely.  
         [0056]    In the structure of this embodiment, when the fuel injector  100  starts to be evacuated by a vacuum pump from the high-pressure passage  3 , the control chamber  4 , the valve chamber  51 , the drain port  21 , the spill chamber  22 , the drain passage  2 , the oil sump  7 , the passage  72 , and the displacement amplifying chamber  6  are, in sequence, evacuated through the pinhole  84 . By injecting the fuel from the drain passage  2 , the displacement amplifying chamber  6  is filled with the fuel quickly. After the displacement amplifying chamber  6  is filled with the fuel, openings of the high-pressure passage  3  and the drain passage  2  are plugged using, for example, rubber cups in order to avoid the leakage of fuel from the displacement amplifying chamber  6 . Usually, a protective cup is fitted on the nozzle head of the fuel injector  100  at the factory. When installed in the engine, the fuel injector  100  is secured in a cylinder head of the engine with the high-pressure passage  3  and the drain passage  2  plugged. Subsequently, they are unplugged and connected to fuel pipes.  
         [0057]    The small-diameter piston  18  may fall by its own weight as the time goes by after the engine is stopped. In this case, an amount of fuel equivalent to the fall of the small-diameter piston  18  is supplied to the displacement amplifying chamber  6  from the drain passage  2  through the check valve  8 , thereby resulting in a difficulty in lifting up the small-diameter piston  18 . Specifically, when the engine is started, the dynamic pressure of fuel supplied from the high-pressure passage  3  works to lift up the ball valve  52  and the small-diameter piston  18 . In the absence of the pinhole  84 , the displacement amplifying chamber  6  is closed completely, thereby holding the small-diameter piston  18  from being lifted up. Therefore, the ball valve  52  is allowed to move from the high-pressure seat  54  slightly, but does no rest on the drain seat  53 . This causes the fuel in the high-pressure passage  3  to continue to flow into the drain passage  2 , so that a desired pressure (e.g., 10 to 20 Mpa) is not reached in the control chamber  4 , thus encountering a difficulty in starting the engine.  
         [0058]    In the structure of this embodiment, the pinhole  84  is formed in the flat valve  81  of the check valve  8 , so that the fuel in the displacement amplifying chamber  6  flows into the drain passage  2  through the pinhole  84  quickly, thereby allowing the small-diameter piston  18  and the ball valve  52  to be lifted up. Thus, when the engine is started, the ball valve  52  is seated on the drain seat  53  quickly, thereby enabling proper fuel injection.  
         [0059]    In the embodiment as described above, the conical spring  82  is used to press the flat valve  81  of the check valve  8  against the lower end of the large-diameter piston  17 , but a circular short spring may alternatively be used. For example, a spring disc  86 , as shown in FIGS.  4 ( a ) and  4 ( b ), may be used which consists of an annular plate and a tongue  87  which extends from an inner periphery of the annular plate in a radius direction and is bent at a given angle.  
         [0060]    While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments witch can be embodied without departing from the principle of the invention as set forth in the appended claims. For example, the three-way valve  5  is used to open and close the spray hole  11  formed in the head of the nozzle body B 1 , however, the invention is not limited to the same. Another known mechanism such as a two-way valve may be used to open and close the spray hole  11 . Further, the piezoelectric actuator  14  is implemented by a piezoelectric device, however, another element such as a solenoid or a magnetostrictor may be used.