Abstract:
A fuel system for a diesel engine having a plurality of combustion chambers, the engine having ignition cackle occurring in at least one combustion chamber includes a standard fuel injector being associated with each of the non-cackling combustion chambers, and a non-standard fuel injector being associated with each of the cackling combustion chambers, each of the non-standard fuel injectors having an increased pilot volume of fuel, the increased pilot volume of fuel having a quantity of fuel therein for injection into the associated combustion chamber. A non-standard fuel injector and a method for affecting cackle are also included.

Description:
[0001]    The present application claims the benefit of U.S. Provisional application Ser. No. 60/179,360, filed Jan. 31, 2000 and incorporated herein in its entirety by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates generally to hydraulically-actuated fuel injection systems and, more particularly, to devices and methods for eliminating the phenomenon known as “cackle”.  
         BACKGROUND OF THE INVENTION  
         [0003]    Hydraulically actuated electronically controlled unit injectors (HEUI injectors) are known in the art. See U.S. Pat. No. 5,492,098 to Hafner et al., incorporated herein by reference. Engines with HEUI injectors are known to produce a noise referred as cackle when the fuel injected during the pilot or pilot portion of an injection event is insufficient to initiate combustion. The main injection portion of the injection event that follows such pilot injection typically produces a higher rate of pressure rise than is experienced following normal pilot injection. The higher rate of pressure rise during main injection results in an audible cackle sound that can be misinterpreted as a major engine mechanical problem. The cackle phenomenon is not harmful to the engine, but the sound has caused user concern and has resulted in unnecessary visits to dealers with perceived engine problems which in turn has resulted in increased (and unnecessary) warranty costs for engines in the field with HEUI injectors.  
           [0004]    Cackle is a phenomenon which occurs if the pilot injection for a particular cylinder is compromised due to incomplete fill of the fuel pumping volume (the high pressure pump chamber) in the HEUI injector. This manifests itself in insufficient fuel injected into the cylinder to initiate combustion with the pilot injection alone and consequently the ensuing main injection yields a higher rate of cylinder pressure rise than other cylinders, thereby causing a non-rhythmic noise that is frequently misdiagnosed as a major mechanical problem. The partial noise that is frequently misdiagnosed as a major mechanical problem. The partial fill of the injector pumping volume that results in cackle may be caused by one of the following:  
           [0005]    low fuel pressure resulting from fuel pump, pressure regulating valve or check valve problems;  
           [0006]    high fuel pressure fluctuation (adverse fuel rail dynamics) caused by disturbances of nearby cylinders (cylinder  6  to cylinder  8 , for example); or  
           [0007]    other deficiencies, for example, combustion gas leakage past a copper injector gasket.  
           [0008]    Note that the firing order in a typical V 8  type engine is  1 - 2 - 7 - 3 - 4 - 5 - 6 - 8 .  
           [0009]    The number six cylinder and the number eight cylinder are immediately adjacent to one another on the left bank of cylinders. Accordingly, it is the high pressure fuel spill of the number six cylinder immediately preceding the filling of the pumping volume of the number eight cylinder that can cause high fuel pressure fluctuation, resulting in the partial fill of the pumping volume of the number eight cylinder. This results in cackle experienced in the number eight cylinder. Note further that such engines have incorporated substantially identical injectors to serve each of the cylinders.  
           [0010]    In the past, certain engines have utilized a fuel pressure accumulator to eliminate the cackle problem. Engines, including the engine described hereinafter, have incorporated check valves, a dead-headed fuel system, and fuel system calibration to help reduce cackle. However, these expedients still have not fully resolved the cackle problem and there is still a need for a solution to the cackle problem.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention substantially meets the aforementioned needs of the industry. Controlling the quantity of fuel injected during the pilot portion of the injection event has been determined to be the critical factor in eliminating the cackle sound. Installing an injector with a long lead in the cackling cylinder assures an adequate quantity of fuel injected during the pilot portion of the injection event to ensure ignition of the pilot portion and thereby eliminating the cackle sound that occurs during the ensuing portion of the injection event. The injector of the present invention increases injector lead and thereby increases the quantity of fuel injected during the pilot portion of the injection event. This cures cackle because it assures that sufficient fuel is injected initially during the injection event to support combustion during the pilot portion of the injection event, without regard to adverse fuel rail dynamics.  
           [0012]    The present invention is a fuel system for a diesel engine having a plurality of combustion chambers, the engine having ignition cackle occurring in at least one combustion chamber includes a standard fuel injector being associated with each of the non-cackling combustion chambers, and a nonstandard fuel injector being associated with each of the cackling combustion chambers, each of the non-standard fuel injectors having an increased pilot volume of fuel, the increased pilot volume of fuel having a quantity of fuel therein for injection into the associated combustion chamber. The present invention is also a non-standard fuel injector and a method for affecting cackle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a cross sectional view of the HEUI injector of the present invention;  
         [0014]    [0014]FIG. 2 is a sectional view of the portion of the injection of FIG. 1 within the circle  2  during the fill stage prior to an injection event;  
         [0015]    [0015]FIG. 3 is the injector of FIG. 2 during the pilot portion of an injection event;  
         [0016]    [0016]FIG. 4 is a sectional view of the injector of FIG. 2 during the pressure relief portion of the injection event;  
         [0017]    [0017]FIG. 5 is a sectional depiction of the injector of FIG. 2 during the main injection portion of the injection event;  
         [0018]    [0018]FIG. 6 is a graphic depiction of cylinder pressure v. crank angle of an eight cylinder, V-type engine for cylinders  2 ,  4 ,  6  and  8  all on the left bank of cylinders of a prior art fuel system; and  
         [0019]    [0019]FIG. 7 is a schematic representation of the fuel system of the present invention where cylinder  8  is the cackling cylinder. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    The fuel system of the present invention is shown generally at  10  of FIG. 7. The injector of the present invention is shown generally at  15  in the figures. Referring to FIG. 1, a standard injector  14  and the non-standard injector  15  of the present invention are preferably hydraulically-actuated unit pump-injectors (HEUI injector). It should be noted that the injector  15  is a modification of the injector  14  and the general description below describes both of the injectors  14 ,  15 . The inventive modifications included in the non-standard injector  15  are noted below. The injectors  14 ,  15  generally include an electrical actuator and control valve assembly  42 , a body  44 , a plunger and barrel assembly  46 , and an injection nozzle assembly  48  having a movable flow check  50  and one or more fuel spray orifices  52 .  
         [0021]    The actuator and valve assembly  42  serves as a means or device for selectively communicating relatively high pressure actuating fluid (preferably engine lubricating oil) from a manifold  43  (see FIG. 7) to the respective injectors  14 ,  15  in response to receiving an electrical control signal from an injection system electronic control module  45 . The assembly  42  includes an electrical actuator  54  and a single actuating fluid control valve  56 . For example, the actuator  54  may be an on/off-solenoid and the valve  56  may be a poppet valve connected to a movable armature of the solenoid.  
         [0022]    The plunger and barrel assembly  46  includes a barrel  58 , a reciprocal fuel pump plunger  60 , and a spill control device  62  for temporarily or intermittently spilling fuel during the pumping stroke of the plunger  60 . The spill control device  62  spills a portion of fuel contained in the high pressure fuel circuit of the injectors  14 ,  15  between the plunger  60  and injection nozzle assembly  48 . The barrel  58  and the plunger  60  each define in part the variable volume high pressure fuel pump chamber  66 . The chamber  66  comprises the variable injector pumping volume referred to above.  
         [0023]    [0023]FIG. 1 depicts an actuating fluid piston  64  integrally connected to the plunger  60 . Alternatively, the piston  64  may be a separate movable component positioned adjacent to the plunger  60 . Preferably, the actuating fluid piston  64  has a larger effective diameter than the fuel pump plunger  60  in order to effect a pressure intensification of the fuel contained in the high pressure fuel pump chamber  66  and in the rest of the high pressure fuel circuit of the injectors  14 ,  15  leading to the spray orifices  52 .  
         [0024]    Preferably, the spill control device  62  temporarily or intermittently spills a portion of the fuel from the high pressure, variable volume, pump chamber  66  (defined by the plunger  60  in cooperation with the bore of the barrel  58 ) during each downward or pumping stroke of the plunger  60 .  
         [0025]    Referring to FIGS.  1 - 5 , the spill control device  62  is depicted. The spill control device  62  includes at least one spill port  68  defined in the barrel  58  and at least one spill passage  70  defined in the movable plunger  60  for intermittently communicating a portion of the fuel from the pump chamber  66  with the spill port  68  during the pumping stroke of the plunger  60 . The spill port  68  intersects the plunger bore  67  of the barrel  58  in which the plunger  60  reciprocates. The spill port  68  also communicates with a relatively low pressure fuel circuit  71  (see FIG. 7) supplying fuel to the injectors  14 , 15 .  
         [0026]    The spill passage  70  includes one or more internal axial passages  72  defined in the plunger  60  and a circumferential outer groove or annular slot  74  encircling the plunger  60 . The groove  74  is preferably generally cylindrical in shape. The groove  74  is spaced from the plunger head  70  of the plunger  60 . The width dimension of the groove  74  and the distance dimension of the groove  74  from the plunger head  70  affect injector lead. The plunger head  70  faces the fuel pump chamber  66  and defines in part the fuel pump chamber  66 . The passages  72  are arranged in continuous fluid communication between the fuel pump chamber  66  and the circumferential groove  74 . The circumferential groove  74  is arranged to be in intermittent fluid communication with the spill port  68 , the barrel  58  during the pumping stroke of the plunger  60 . The groove  64  defines a land  69  that extends between the plunger head  70  and the groove  74  and a trailing land  71  disposed upward of the groove  74  in the figures. The width dimension of the land  69  affects injector lead.  
         [0027]    The axial distance between the upper edge (the edge furthest from the fuel pump chamber  66 ) of the spill port  68  and the leading edge (closest to the fuel pump chamber  66 ) of the circumferential groove  74  controls in part the initial rate of fuel injection (the pilot injection) of an injection event. The axial distance may be referred to as lead. As indicated above, other factors also affect lead, including, for example, the distance dimension between the groove  74  and the plunger head  70 , the width dimension of the groove  74 , and the distance dimension of the spill port  68  from the plunger head to when the plunger  60  is fully retracted. The standard fuel injector  14  has a standard lead dimension defined within known manufacturing tolerances.  
         [0028]    By changing the geometry of the plunger  60  and the barrel  58  (and the spill port  68 ), the quantity of fuel injected during the pilot portion of the injection event is variable. After commencement of the compressing downstroke of the plunger  60 , a relatively longer lead of the non-standard injector  15  of the present invention delays spilling of fuel pressure to the spill port  68 , thereby ensuring a desired (generally increased) volume of fuel is injected into the cylinder combustion chamber during the pilot portion, as will be described in greater detail below. This volume of fuel is adequate to ensure combustion during the pilot portion of the injection event.  
         [0029]    The operation of the fuel injectors  14 ,  15  of the present invention is depicted sequentially in FIGS.  2 - 5 . As depicted in FIG. 6, the injection event generally has a pilot portion that generally is left of about 7° after top dead center (TDC)crank angle followed by main injection that is generally right of about 7° AFTER TDC crank angle. Referring to FIG. 2, the plunger  60  is fully retracted and the land  69  of the plunger  60  covers the spill port  68  of the barrel  58 . The fuel inlet check valve  75  is open, admitting relatively low pressure fuel to the fuel pump chamber  66 . The high pressure fuel check valve  76  is closed, sealing off the fuel pump chamber  66 . The fuel in the fuel pump chamber  66  flows through the passages  72  to flood the groove  74 .  
         [0030]    Referring to FIG. 3, when the injection system electronic control module energizes the solenoid  54  of the respective injectors  14 ,  15 , the control valve  56  is pulled off its high pressure seat to admit high pressure actuating fluid (typically engine oil) into the injectors  14 ,  15 . The actuating fluid hydraulically actuates or directly drives the plunger  60  downward to begin a pumping stroke. Fuel in the fuel pump chamber  66  is pressurized by the plunger  60  so that the fuel pressure increases in the fuel pump chamber  66 . The increasing pressure closes the fuel inlet check valve  75  and opens the high pressure fuel check valve  76 . When the increasing pressure of the fuel reaches the valve opening pressure of the injection nozzle assembly  48 , the check  50  unseats to begin the initial pilot or pilot injection of fuel through the spray orifices  52 . The cylinders  1 - 8  are depicted in FIG. 7, a standard injector  14  being associated with cylinders  1 - 7  and a non-standard injector  15  being associated with the cackling number  8  cylinder. Referring to the curve for cylinders  2 ,  4 ,  6  in FIG. 6, this initial portion of the injection of fuel comprising the pilot portion occurs between about 10° BEFORE TDC crank angle and 7° AFTER TDC crank angle. It should be noted that during the same crank angle span, the cylinder pressure trace for cylinder  8  (the cackling cylinder) is less than for the aforementioned cylinders when cylinder  8  is served by a prior art standard injector  14  as distinct from the non-standard injector  15  of the present invention. This indicates that the fuel supply for cylinder  8  is insufficient to cause combustion during the pilot portion of the injection event.  
         [0031]    Such insufficiency could occur in any cylinder, but cylinder number  8  in a V 8  type engine is particularly susceptible to a reduced quantity for pilot injection when cylinder  8  is served by a prior art standard injector  14 . This results from the fact that the left bank of cylinders of a V 8  engine being cylinders number  2 ,  4 ,  6  and  8 , as depicted in FIG. 7, and the firing order being  1 - 2 - 7 - 3 - 4 - 5 - 6 - 8  means that the cylinder immediately next to cylinder number  8  (cylinder number  6 ) fires immediately prior to cylinder number  8 . The result may be insufficient fuel to completely fill the pumping volume of the fuel pump chamber  66  resulting in insufficient fuel injected during the pilot portion of the injection event to initiate combustion in the cylinder combustion chamber. This insufficiency will produce cackle during the main injection portion of the injection event, as described below.  
         [0032]    Referring to FIG. 4, as the plunger  60  continues moving downwardly on its pumping stroke, the circumferential groove  74  of the plunger  60  communicates with the spill port  68  of the barrel  58  so that a portion of the high pressure fuel in the pump chamber  66  is spilled into the port  68 . The fuel pressure in the fuel pump chamber  66  is thereby temporarily reduced. The high pressure check valve  76  closes. This causes the check  50  (FIG. 1) to seat, thereby ceasing delivery of fuel via orifices  52 . The inlet check valve  75  remains closed. Referring again to FIG. 6 in the curves for cylinders  2 ,  4 , and  6 , the temporary reduction in pressure occurs generally between about 5 and 10° AFTER TDC crank angle. During the same crank angle duration, the trace for cylinder  8  indicates that the pressure fall off is much greater as a result of there having been insufficient fuel injected during the pilot portion of the injection event to initiate combustion when cylinder  8  is served by a prior art standard injector  14 .  
         [0033]    Referring to FIG. 5, as the plunger  68  continues moving downwardly on its pumping stroke, the trailing land  71  of the plunger  60  blocks the spill port  68  and the circumferential groove  74  no longer is in fluid communication with the spill port  68 . The fuel pressure in the fuel pump chamber  66  again rises, opening the high pressure check valve  76  to again unseat the check  50  and begin the main portion of the injection event by injecting fuel through the orifices  52 . Referring to FIG. 6, the rise in the cylinder pressure for cylinders  2 ,  4 , and  6  occurs initially at about 70 AFTER TDC and continues to about 15° AFTER TDC. It is noted that the trace for cylinder  8  indicates that the rise in cylinder pressure is delayed several degrees as compared to the rise for cylinders  2 ,  4 , and  6  when cylinder  8  is served by a prior art standard injector  14 . The rise for cylinder  8  is also much steeper and peaks several degrees before the traces for cylinders  2 ,  4 , and  6  at a significantly higher cylinder pressure. The resulting combustion in the chamber at high cylinder pressure produces the objectionable cackle sound during the main portion of the injection event.  
         [0034]    The fuel injector  15  of the present invention has a longer lead than the standard injectors  14  used in cylinders  1 - 7  or in any cylinder in which cackle is not a problem. The expedient of installing a non-standard injector  15  with a longer lead in any cylinder that exhibits cackle effectively eliminates the cackle problem without inducing greater particulate emissions or other adverse engine effects. Tests have shown that the installation of the non-standard injector  15  of the present invention in cylinder  8  results in the trace for cylinder  8  being substantially coincident with the traces of cylinders  2 ,  4 , and  6 , the non-cackling cylinders on the left bank.  
         [0035]    The effect of increasing the lead of the non-standard injector  15  relative to the standard injector  14  is to increase the length of stroke of plunger  60  that occurs between the initiation of the fuel injection event and the point at which the circumferential groove  74  is in fluid communication with the spill port  68 . Such longer stroke ensures that adequate fuel is injected during the pilot portion of the injection event to initiate combustion.  
         [0036]    There are a number of different ways in which the lead of the non-standard injector  15  can effectively be increased. A first way is to machine the circumferential groove  74  at a greater distance from the plunger head  70 . A second way is to increase the distance of the point of intersection of the spill port  68  with the bore of the barrel  58  to the plunger head  70  (and coincidentally, the distance to the groove  74 ) when the plunger  60  is in its full retracted position. Increasing the noted distance effectively delays the spill that occurs when the groove  74  intersects the spill port  68  A normal lead length is preferably approximately 0.4 mm. An increased lead length sufficient to ensure combustion during the pilot portion of the injection event is preferably a lead length of approximately 0.45 mm.