Patent Publication Number: US-6908042-B2

Title: Fuel injector

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a pressure intensifying fuel injector for use in a vehicle diesel engine or the like and, in particular, to a fuel injector which allows air bleeding, for example, during startup. 
   DESCRIPTION OF THE RELATED ART 
   There are two types of fuel injectors for use in vehicle diesel engines or the like: accumulation-type fuel injectors injecting fuel accumulated at a predetermined pressure, and pressure-intensifying-type fuel injectors pressurizing fuel when injecting it. 
   In either type of fuel injectors, the fuel system is subject to air intrusion when, for example, the fuel injector is mounted in the engine, when maintenance is performed thereon, or when the piping is replaced. Thus, it is necessary to perform air bleeding when cranking the engine. 
   There has been proposed an accumulation-type fuel injector in which fuel at a predetermined pressure is supplied to the fuel injector with a predetermined timing, wherein an electromagnetic valve for opening and closing the injection port of the fuel injector is operated with a timing different from the above-mentioned predetermined timing to thereby automatically effect air bleeding (See Japanese Patent Application Laid-Open No. 10-252611). 
   In the case of a pressure-intensifying-type fuel injector, however, the system for supplying fuel to the pressure intensifying chamber and the operating fluid system for operating the plunger of the pressure intensifying chamber are two separate systems, and the electromagnetic valve does not directly opens and closes the needle valve for injecting fuel. Thus, it is impossible to exclusively bleed air by operating the electromagnetic valve. 
   It might be possible to provide an opening/closing valve in the fuel supply passage of a fuel injector and bleed air through this opening/closing valve. In this case, however, it would be necessary to open or close this valve through manual operation or the like at the time of cranking, which means it would be impossible to automatically effect bleeding. Further, the provision of the opening/closing valve would complicate the structure. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above problems in the prior art. It is accordingly an object of the present invention to provide a pressure-intensifying-type fuel injector which allows air bleeding to be conducted automatically and with a simple structure. 
   To achieve the above object, there is provided, in accordance with the present invention, a fuel injector comprising a pressure intensifying chamber communicating with a fuel supply passage through a check valve, a plunger for pressure-intensifying fuel introduced into the pressure intensifying chamber, and a needle valve for injecting the fuel pressure-intensified in the pressure intensifying chamber through an injection port, wherein there is provided in the fuel supply passage a throttle passage normally communicating with a fuel drain passage. 
   In this construction, when fuel is supplied to the fuel supply passage at the time of cranking, the pressure in the fuel supply passage increases, and a fuel flow from the throttle passage to the fuel drain passage is formed. With this fuel flow, the air existing in the fuel supply passage is forced into the drain passage. Since the fuel is pressure-intensified in the pressure intensifying chamber, the fuel supplied to the fuel supply passage is at a low pressure of approximately several atmospheres. Thus, it is possible to perform air bleeding while keeping the amount of fuel leaked from the throttle passage small. After the air bleeding, the fuel from the fuel supply passage continues to flow to the drain passage by way of the throttle passage. This fuel circulates by way of the fuel tank, etc. to be supplied to the fuel supply passage again. Thus, the amount of fuel leaked to the drain passage through the throttle passage is not so large, and the throttle passage provides an aperture large enough to allow air bleeding. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view showing a fuel injector according to an embodiment of the present invention in a state prior to injection start; 
       FIG. 2  is a schematic diagram showing a common-rail-type fuel injection device to which the fuel injector of this embodiment of the present invention is applied; 
       FIG. 3  is a sectional view showing the fuel injector of this embodiment of the present invention at the time of injection start; and 
       FIG. 4  is a sectional view showing a fuel injector according to another embodiment of the present invention in a state prior to injection start. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   First, the construction of a fuel injector  1  will be described. In  FIG. 1 , successively arranged from below in the fuel injector  1  are an injection mechanism  2 , a pressure intensifying mechanism  3 , and an electromagnetic valve  4 . This fuel injector  1  is mounted in an engine, such as a diesel engine, in an attitude in which the injection mechanism  2  is directed downwards as shown in the drawing. This downwardly directed position is not restricted to the vertical one. The injection mechanism  2  may also be directed obliquely downwards. 
   The injection mechanism  2  has a nozzle body  12  at the lower end of which an injection port  11  is open. In the nozzle body  12 , an axially slidable needle  13  is biased by a presser spring  14 . The nozzle body  12  comprises a first body  15 , a second body  16 , and a third body  17 , which are successively arranged from below in that order. These bodies are put into a cylindrical casing  18  one by one. 
   The first body  15  is a cylindrical member whose forward end portion is relatively narrow and which has a shoulder portion  21 . The shoulder portion  21  abuts a step portion  22  of the casing  18 , and the forward end portion of the first body  15  having the injection port  11  protrudes downwardly. Provided in the first body  15  are a conical valve seat  23 , a storage portion  24  for high-pressure fuel, and a slide hole  25  for the needle  13 . A needle valve is formed by the valve seat  23  of the first body  15  and the needle  13 . 
   The needle  13  comprises a conical valve portion  131  facing the valve seat  23 , a small diameter portion  132 , a step portion  133 , a large diameter portion  134 , a neck portion  135 , and a spring seat  136 , which are arranged in that order from below. The second body  16  includes a retaining hole  161  for the neck portion  135  of the needle  13 , and an accommodating chamber  162  for the presser spring  14 . The presser spring  14  in the accommodating chamber  162  is loaded into the casing  18 , with the third body  17  thereon so as to downwardly bias the needle  13 . 
   A supply passage  26  for high-pressure fuel extends through the third body  17  and the second body  16  so as to be offset from the centers of these bodies. This supply passage  26  extends through the first body  15  to communicate with the storage portion  24  for high-pressure fuel. 
   The injection mechanism  2 , constructed as described above, operates as follows. When high-pressure fuel is supplied to the storage portion  24  by way of the supply passage  26 , the step portion  133  of the needle  13 , etc. receive pressure, with the result that a pressurizing force counteracting the biasing force of the presser spring  14  acts on the needle  13 . When the pressure of the high-pressure fuel reaches a predetermined level, the pressurizing force of the high-pressure fuel and the biasing force of the presser spring  14  are in equilibrium with each other. The needle  13  then moves upwards, and the valve portion  131  at the forward end thereof is separated from the valve seat  23 , with the result that high-pressure fuel at a predetermined pressure is injected through the injection port  11 . As long as high-pressure fuel continues to be supplied to the storage portion  24 , the injection of high-pressure fuel at a predetermined pressure through the injection port  11  continues. When high-pressure fuel ceases to be supplied to the storage portion  24 , and the pressure in the storage portion  24  decreases, the presser spring  14  acting on the needle  13  causes the valve portion  131  at the forward end of the needle to be seated on the valve seat  23 , and the injection of fuel through the injection port  11  is stopped. 
   The fuel leaking through the slide portion between the slide hole  25  of the first body  15  and the large diameter portion  134  of the needle  13  passes through the gap between the retaining hole  161  and the neck portion  135 , reaches the accommodating chamber  162 , reaches an annular passage  27  between the casing  18  and the second body  16  by way of a passage  163 , and communicates with a fuel supply passage  44  at low pressure positioned above. 
   The pressure intensifying mechanism  3  positioned above the injection mechanism  2  includes a cylinder body  31 , which contains an axially slidable plunger  32  joined to a pressure intensifying piston  33 , with a return spring  34  acting on the plunger  32 . The cylinder body  31  comprises a fourth body  35  and a fifth body  36 , which are successively loaded into the casing  18 . A threaded portion  361  of the fifth body  36  and a threaded portion  181  of the casing  18  are threadedly engaged with each other. 
   Formed in the fourth body  35  is a pressure intensifying chamber  41  in the form of a small diameter hole, into which the plunger  32  is slidably fitted. Formed in the fifth body  36  is a pressurizing chamber  42  in the form of a large diameter hole, into which the pressure intensifying piston  33  is slidably fitted. The plunger  32  has at its upper end a head portion  321 , which is engaged with the pressure intensifying piston  33 . Further, the return spring  34  is arranged between the head portion  321  of the plunger  32  and the upper end of the fourth body  35 . 
   In the side surface the portion of the casing  18  corresponding to the fourth body  35 , there is formed a fuel supply port  43 . Over the fourth body  35  and the third body  17 , there is formed a fuel supply passage  44  extending from the supply port  43  to the pressure intensifying chamber  41 . This fuel supply passage  44  is formed by an annular space  441  defined by a recess in the outer periphery of the fourth body  35 , a lateral passage  442  in the fourth body  35 , a longitudinal passage  443  in the fourth body  35 , and a radial passage  171  in the top surface of the third body  17 . There is arranged a check valve  45  which vertically operates at the portion where the longitudinal passage  443  communicates with the radial passage  171 . The forward direction for the check valve  45  is the direction toward the pressure intensifying chamber  41 . Further, the radial passage  171  of the third body  17  also communicates with the supply passage  26  for high-pressure fuel. 
   Drain from the pressure intensifying chamber  41  for the plunger  32  flows into the accommodating chamber  362  accommodating the return spring  34 , the accommodating chamber  362  forming the pressurizing chamber  42  of the fifth body  36 . This accommodating chamber  362  communicates with a first drain passage  46 , which is formed by a lateral groove  461  of the fourth body  35  and a longitudinal passage  462  of the fifth body  36 , and communicates with a discharge port  58  by way of a second drain passage  63  described below. 
   The operation of the pressure intensifying mechanism  3 , constructed as described above, is as follows. As will be described in detail below, when an operating fluid is supplied to the pressurizing chamber  42 , the fuel in the pressure intensifying chamber  41  is pressurized by the pressure intensifying ratio which is determined by the ratio of the outer diameter of the pressure intensifying piston  33  to the outer diameter of the plunger  32 . Since the check valve  45  is closed, the high-pressure fuel pressurized in the pressure intensifying chamber  41  flows to the supply passage  26 . When the operating fluid is discharged from the pressurizing chamber  42 , the pressure intensifying piston  33  and the plunger  32  are raised by the biasing force of the return spring  34 , and the check valve  45  is opened, with the result that fuel is introduced into the pressure intensifying chamber  41  by way of the fuel supply passage  44  and the supply port  43 . 
   The fuel leaked in the injection mechanism  2  flows from the annular passage  27  between the second body  16  and the casing  18  to the fuel supply passage  44  by way of an annular passage  47  between the third body  17  and the casing  18  and an annular passage  48  between the fourth body  35  and the casing  18 . The outer diameter of the third body  17  in the form of a short cylinder is larger than the outer diameter of the second body  16  and the outer diameter of the portion of the fourth body  35  extending up to the annular space  441 , and the annular passage  47  has a minimum gap for allowing passage of the leaked fuel. Due to this third body  17 , the second body  16  is maintained in a position in which it extends along the axis. 
   The construction and operation of the electromagnetic valve  4  for supplying and discharging operating fluid to and from the pressurizing chamber  42  will be described. The fifth body  35  has at its top a block  51 . The electromagnetic valve  4  comprises a valve plug  52 , a yoke  53 , and a solenoid  54 , which are accommodated in the block  51 , and is formed as a three-way two-position switching valve. The block  51  has a valve hole  55  extending perpendicular to the axial direction. Open in the valve hole  55  are an operating fluid supply port  56 , an input/output port  57  communicating with the pressurizing chamber  42 , and a discharge port  58  communicating with a fuel tank or a recovery device. The valve plug  52  is slidably fitted into the valve hole  55 . A presser spring  59  acts on the yoke  53  connected to the valve plug  52 , whereby a first valve  60  between the valve plug  52  and the block  51  is closed, and a second valve  62  between the valve plug  52  and a valve hole partition  61  is open. In this state, the input/output port  57  communicates with the discharge port  58  by way of a second drain passage  63  formed by the inner periphery of the valve hole partition  61  and the passage of the side surface of the yoke  53 . When the yoke  53  connected to the valve plug  52  is attracted by the solenoid  54 , the second valve  62  is closed, and the first valve  60  is opened. In this state, the supply port  56  communicates with the input/output port  57 , and the operating fluid is introduced into the pressurizing chamber  42 . 
   The first drain passage  46  of the pressure intensifying mechanism  3  communicates with the discharge port  58  through the second drain passage  63  of the electromagnetic valve  4 . As will be described below, a fuel is used as the operating fluid for the pressurizing chamber  42  of the pressure intensifying mechanism  3 , so that the first drain passage  46  and the second drain passage  63  communicate with each other, and the leak is returned to a common fuel tank or recovery device. 
   The fuel supply passage  44  of the pressure intensifying mechanism  3  communicates with the first drain passage  46  through a throttle hole  65 . This throttle hole  65  consists of a linear hole formed directly above the annular space  441  of the fuel supply passage  44 , and is open on a lateral groove  461  of the first drain passage  46 . This throttle hole  65  may also be a lateral hole which is open on the lateral groove  461  from the upper end of the annular space  441 . Further, it may also be a hole in the fifth body  36  extending from the upper end of the annular space  441  obliquely to the longitudinal passage  462 . 
   This throttle hole  65  constantly leaks low-pressure fuel from the supply port  43 . When the fuel contains some air, it is possible to allow the air to pass with the leakage of the fuel. Thus, the throttle hole  65  is adjusted such that air is allowed to pass with the leakage of fuel and that the amount of leak fuel passing the first drain passage  46  and the second drain passage  63  is somewhat increased. This throttle hole  65  forms a throttle passage normally communicating with the fuel drain passage. 
     FIG. 2  is a schematic diagram illustrating a common rail type fuel injection device  100  to which the fuel injector  1  of  FIG. 1  is applied. The fuel injection device  100  is provided with one or more fuel injectors  1  respectively mounted in the cylinder heads of an engine (not shown), and comprises an operating fluid circulation system  101  for supplying fuel to the fuel injectors  1  as the operating fluid and recovering it therefrom, a fuel supply system  102  for supplying fuel to the fuel injectors  1 , and a control device  103  for controlling the opening and closing of the electromagnetic valves  4  of the fuel injectors  1 . 
   The operating fluid circulation system  101  is formed by a fuel supply pump  110 , a high-pressure pump  111 , a common rail  112 , a recovery device  113 , etc. The fuel supply pump  110  transfers fuel in a fuel tank  114  under pressure to the high-pressure pump  111 . The high-pressure pump  111  pressurizes the fuel, for example, to approximately 200 atmospheres, and the pressurized fuel is transferred under pressure to the common rail  112 . The fuel stored in the common rail  112  in a pressurized state is supplied to the pressurizing chamber  42  (See  FIG. 1 ) by way of the supply port  56  by the operation of the electromagnetic valve  4 . The operating fluid discharged from the discharge port  58  by the operation of the electromagnetic valve  4  is recovered by the recovery device  113  as fuel, and the recovered fuel is recirculated by the high-pressure pump  111 . 
   The fuel supply system  102  is formed by a pump  121  and a valve  122 . The pump  121  pressurizes the fuel in the fuel tank  114  to approximately several atmospheres, and transfers the fuel under pressure to the supply port  43  of each fuel injector  1 . The valve  122  adjusts the amount of fuel supplied to the fuel injectors  1 . The control device  103  generates a control signal for controlling the opening and closing of the electromagnetic valve  4  of each fuel injector  1 . 
   Provided in each fuel injector  1  is the throttle hole  65  which causes the fuel supplied from the supply port  43  to be transmitted to the discharge port  58  by way of the drain passages  46  and  63  (See FIG.  1 ). Thus, part of the fuel from the fuel supply system  102  flows to the discharge port  58  by way of the throttle hole  65 . 
   Next, the operation of the fuel injector  1 , constructed as described above, will be described with reference to  FIGS. 1 and 3 .  FIG. 1  shows the operation state of the fuel injector  1  prior to injection, and  FIG. 3  shows the operation state thereof at the time of injection. 
   The fuel injector  1  is assembled as shown in  FIG. 1 , and mounted in the fuel injection device  100  as shown in FIG.  2 . At the time of mounting, the interior of the fuel injector  1  is filled with air. 
   In  FIG. 1 , prior to injection, low-pressure fuel is supplied from the supply port  43 . The fuel supplied from the supply port  43  is conveyed to the pressure intensifying chamber  41  after passing the annular space  441 , the lateral passage  442 , the longitudinal passage  443 , and the check valve  45 . Further, it passes the supply passage  26  to fill the interior of the storage portion  24 . In this filling process, the air existing in the fuel passage in the injection mechanism  2  or the pressure intensifying mechanism  3  is forced out by the fuel and rises through the passage in the fuel injector  1 , which is vertically arranged. The rising air passes through the open check valve  45  and gathers in the annular space  441 . The throttle hole  65  is open above the annular space  441 , and the air having reached the annular space  441  is discharged to the first drain passage  46  by way of the throttle hole  65 . Since the first drain passage  46  and the second drain passage  63  communicate with the discharge port  58 , the air is discharged to the exterior of the fuel injector  1 . As a result, the interior of the fuel injector  1  is filled with fuel only. 
   As shown in  FIG. 3 , at the time of injection, the solenoid  54  of the electromagnetic valve  4  is energized, and the yoke  53  is attracted, causing the valve plug  52  to move to the right as seen in the drawing. Then, the first valve  60  is opened, and the second valve  62  is closed, with the result that the supply port  56  and the input/output port  57  communicate with each other, causing operating fluid to be introduced into the pressurizing chamber  42 . The fuel in the pressure intensifying chamber  41  is pressurized at a pressure intensifying ratio determined by the ratio of the outer diameter of the pressure intensifying piston  33  to the outer diameter of the plunger  32 . At this time, the check valve  45  is closed, and the high pressure of the pressure intensifying chamber  41  is propagated to the fuel in the storage portion  24  by way of the supply passage  26 . When the high-pressure fuel in the storage portion  24  attains a pressure, for example, of approximately 200 atmospheres and the needle  13  overcomes the biasing force of the presser spring  14  to lift the valve portion  131  from the valve seat  23  by the step portion  133 , etc. receive pressure, with the result that high-pressure fuel is injected from the injection port  11 . The descent of the pressure intensifying piston  33  causes the fuel forced out of the accommodating chamber  362  to be discharged from the discharge port  58  by way of the first drain passage  46  and the second drain passage  63 . 
   When the injection of high-pressure fuel is completed, the solenoid  54  of the electromagnetic valve  4  is changed to the non-energized state, and the valve plug  52  and the yoke  53  are moved to the left as seen in the drawing by the biasing force of the presser spring  59 , causing the first valve  60  to be closed and the second valve  62  to be opened, with the result that the input/output port  57  and the discharge port  58  communicate with each other. Then, the operating fluid, which has been introduced into the pressurizing chamber  42 , is discharged from the discharge port  58 , and the pressure intensifying piston  33  and the plunger  32  are raised by the biasing force of the return spring  34  to return to the position shown in FIG.  1 . The accommodating chamber  362  communicates with the first drain passage  46 , the second drain passage  63 , the second valve  62  in the open state, and the input/output port  57 , so that A most of the operating fluid of the pressurizing chamber  42  circulates through the first drain passage  46  and the second drain passage  63 . 
   When the fuel injector  1  is filled with fuel and remains at rest in this state for a long period of time, air, etc., which have been dissolved in the fuel, will be brought back to the gaseous state. The gas thus generated passes through the supply passage  26  and the check valve  45  and gathers in the annular space  441  having the throttle hole  65 , where the pressure is at the minimum. Thus, when the engine is re-started, the gas generated is also bled from the throttle hole  65  as stated above. 
   The above-described embodiment provides the following advantages.
     (1) Due to the construction in which there is provided a throttle hole  65  that is normally open on the drain passage  46  from the fuel supply passage  44 , bleeding of gases such as air contained in the fuel injector  1  is effected simultaneously with the supply of fuel to the fuel injector  1  when the fuel injector  1  is re-mounted or the engine is started after a long rest. Thus, bleeding can be effected reliably, remarkably reducing the possibility of the fuel injector  1  performing improper injection.   (2) Since the throttle hole  65  is a bypass which is normally open on the drain passage  46 , there is no need to perform control to open and close the throttle hole  65 . The fact that it is a simple opening implies a superior durability. Further, it is free from secular changes.   (3) In  FIG. 1 , the throttle hole  65  is provided between the fuel supply passage  44  and the first drain passage  46  for the plunger  32 . The first drain passage  46  of the plunger  32  and the fuel supply passage  44  leading to the pressure intensifying chamber  41  for the plunger  32  are close to each other, so that it is possible to provide a short throttle hole  65  between them. Thus, the throttle hole  65  can be formed by minimum machining of the existing parts, involving no increase in weight and cost due to additional parts.   (4) In  FIG. 1 , the throttle hole  65  communicates with the discharge port  58  by way of the first drain passage  46  and the second drain passage  63 , so that it is possible to allow the leak fuel from the throttle hole  65  to flow with the leak fuel from the pressure intensifying mechanism  3  and the leak fuel from the electromagnetic valve  4 , making it possible to effect discharge from the throttle hole  65  by a simple route. Thus, there is no need to separately provide a port for recovering the leak fuel from the throttle hole  65 .   (5) In  FIG. 1 , a recess is provided in the outer periphery of the portion of the fourth body  35  extending down to the fuel supply passage  44 , and this recess constitutes the annular space  441  communicating with the fuel supply passage  44 , the throttle hole  65  being open above this annular space  441 . Due to this construction, air gathers in the annular space  441  situated above the fuel supply passage  44 . Since the air gathered in the annular space  441  is bled through the throttle hole  65  which is open above the annular space  441 , the air contained in the fuel is bled reliably.   

   The present invention is not restricted to the above-described embodiment. For example, the following modifications are possible.
     (1) As shown in  FIG. 4 , the present invention is also applicable to a fuel injector  201  of the type in which the pressure intensifying mechanism is not formed by a pressure intensifying cylinder operated by an electromagnetic valve but uses an external force to push down the plunger  32 . In this case, the plunger  32  is connected to a presser bar  211  whose forward end abuts a cam  212 . The cam  212  is adapted to rotate with the rotation of the engine. As the cam  212  rotates, the plunger  32  moves vertically to pressure-intensify the fuel in the pressure intensifying chamber  41 . In this case also, the throttle hole  65  is provided between the fuel supply passage  44  and the first drain passage  46 . The fuel flowing through the first drain passage  46  is discharged through a discharge hole  213  and recovered by a fuel tank or the like.   (2) In the common rail type fuel injection device  100  of  FIG. 2 , it is possible for the fuel from the discharge port  58  in the operating fluid recirculation system  101  to be returned directly to the fuel tank  114  for circulation without passing the recovery device  113 .   (3) In  FIG. 1 , the throttle hole  65  may consist of a throttle passage which is open on the second drain passage  63  and which is arranged side by side with the first drain passage  46 . When the first drain passage  46  is situated above, it is advantageous, in some cases, for the throttle hole  65  to open on the second drain passage  63  than on the first drain passage  46 .