Abstract:
A closed nozzle injector for injecting fuel at high pressure into the combustion chamber of an engine, is provided including a lower supply chamber positioned in the nozzle housing, an injector plunger including a lower guide sized to form a close sliding fit with a nozzle housing to guide the plunger during reciprocal movement, and a plurality of restriction orifices formed in the injector plunger and positioned about the injector plunger to restrict fuel flow from an upper supply chamber to the lower supply chamber. The lower guide is positioned axially between the lower supply chamber and the injection orifices.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to plungers for high pressure fuel injectors, and high pressure fuel injectors, for injecting fuel into an internal combustion engine. 
       BACKGROUND 
       [0002]    In most fuel supply systems applicable to internal combustion engines, fuel injectors are used to direct fuel pulses into the engine combustion chamber. A commonly used injector is a closed-nozzle injector which includes a nozzle assembly having a spring-biased nozzle valve element positioned adjacent the nozzle orifice for resisting blow back of exhaust gas into the pumping or metering chamber of the injector while allowing fuel to be injected into the cylinder. The nozzle valve element also functions to provide a deliberate, abrupt end to fuel injection thereby preventing a secondary injection which causes unburned hydrocarbons in the exhaust. The nozzle valve is positioned in a nozzle cavity and biased by a nozzle spring to block fuel flow through the nozzle orifices. In many fuel systems, when the pressure of the fuel within the nozzle cavity exceeds the biasing force of the nozzle spring, the nozzle valve element moves outwardly to allow fuel to pass through the nozzle orifices, thus marking the beginning of injection. In another type of system, such as disclosed in U.S. Pat. No. 5,676,114 to Tarr et al., the beginning of injection is controlled by a servo-controlled needle valve element. The assembly includes a control volume positioned adjacent an outer end of the needle valve element, a drain circuit for draining fuel from the control volume to a low pressure drain, and an injection control valve positioned along the drain circuit for controlling the flow of fuel through the drain circuit so as to cause the movement of the needle valve element between open and closed positions. Opening of the injection control valve causes a reduction in the fuel pressure in the control volume resulting in a pressure differential which forces the needle valve open, and closing of the injection control valve causes an increase in the control volume pressure and closing of the needle valve. 
         [0003]    U.S. Pat. No. 6,499,467 issued to Morris et al. discloses a servo-controlled needle valve injector which also includes an inner restriction orifice to restrict the flow of fuel from a spring chamber to an inner control volume to create a desired force profile on the needle valve element. Likewise,  FIG. 1  herein shows a similar servo-controlled injector including a plunger with an inner restriction orifice operating as explained in the &#39;467 patent. 
       SUMMARY 
       [0004]    This disclosure provides a closed nozzle injector for injecting fuel at high pressure into the combustion chamber of an engine, comprising an injector body including an upper supply chamber and a nozzle housing, wherein the nozzle housing includes a lower supply chamber, a plunger seat, and injector orifices. An injector plunger is positioned in the nozzle housing for movement between a closed position in abutment against the plunger seat to block fuel flow through the injector orifices and an open position positioned a spaced distance from the plunger seat to permit fuel flow through the injector orifices. The injector plunger includes a lower guide sized to form a close sliding fit with the nozzle housing to guide the injector plunger during reciprocal movement. The lower guide is positioned axially between the lower supply chamber and the injection orifices. The injector plunger further includes a plurality of restriction orifices formed in the injector plunger and positioned symmetrically about the injector plunger to restrict fuel flow from the upper supply chamber to the lower supply chamber. 
         [0005]    The plurality of restriction orifices may be limited to two orifices having central axes positioned in a common plane extending through a longitudinal axis of the injector plunger. The injector plunger may include an upper guide sized to form a close sliding fit with the nozzle housing to create a substantial fluid seal between the upper guide and the nozzle housing, and the plurality of restriction orifices may be formed in the upper guide. The nozzle housing may include a lower bore positioned between the lower supply chamber and the injector orifices to receive the injector plunger. The lower bore may have an outer diameter less than the outer diameter of the lower supply chamber. The lower guide may be positioned in the lower bore. The lower supply chamber may be defined at one end by the upper guide and at an opposite end by one end of the lower bore. The lower supply chamber may include an axial extent greater than an axial extent of the upper guide. Each of the plurality of restriction orifices may be positioned entirely on an opposite diametric side of the injector plunger from another one of the plurality of restriction orifices and in a common transverse plane extending perpendicular to a longitudinal axis of the injector plunger. The nozzle housing may be formed as one-piece and each of the plurality of restriction orifices, the upper guide, and the lower guide may be positioned in the one-piece nozzle housing. The lower guide may include fuel passages sized to permit unrestricted fuel flow through the fuel passages. The plurality of restriction orifices may each be linear passages having a longitudinal axis extending in a plane parallel to a longitudinal axis of the plunger. The injector plunger may further include a plurality of flow passages formed in the upper guide, and each of the plurality of flow passages may connect to, and have a larger cross-sectional flow area than, a respective one of the plurality of restriction orifices. A greater longitudinal portion of the lower bore is preferably positioned between the lower guide and the lower supply chamber than is positioned between the lower guide and the injector orifices. 
         [0006]    This disclosure also provides a closed nozzle injector for injecting fuel at high pressure into the combustion chamber of an engine, comprising an injector body including an upper supply chamber and a nozzle housing, wherein the nozzle housing includes a lower supply chamber, a plunger seat, and injector orifices. An injector plunger is positioned in the nozzle housing for movement between a closed position in abutment against the plunger seat to block fuel flow through the injector orifices and an open position positioned a spaced distance from the plunger seat to permit fuel flow through the injector orifices. The injector plunger includes a lower guide sized to form a close sliding fit with the nozzle housing to guide the injector plunger during reciprocal movement and an upper guide sized to form a close sliding fit with the nozzle housing to create a substantial fluid seal between the upper guide and the nozzle housing. The injector plunger further includes a plurality of restriction orifices formed in the upper guide and positioned about the injector plunger. The plurality of restriction orifices are sized to restrict fuel flow from the upper supply chamber to the lower supply chamber. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]      FIG. 1  is a cross-sectional view of a portion of a prior art conventional injector showing the nozzle valve assembly and plunger; 
           [0008]      FIG. 2  is an expanded cross-sectional view of a portion of the fuel injector of the present disclosure showing the nozzle assembly including the balanced and guided plunger; 
           [0009]      FIG. 3  is a perspective view of a portion of the plunger showing the lower guide; 
           [0010]      FIG. 4   a  is a side view of a portion of the plunger showing the upper guide; 
           [0011]      FIG. 4   b  is a cross-sectional view of the plunger taken along plane  4   b - 4   b  in  FIG. 4   a;    
           [0012]      FIGS. 5   a  and  5   b  are views within of cylinder of an engine facing upwardly showing the spray pattern of fuel from injector orifices of a conventional injector ( FIG. 1 ) and the injector of  FIG. 2 , respectively; and 
           [0013]      FIGS. 6   a  and  6   b  are injection rig measurement data comparing the shot-to-shot end of injection variation of a conventional injector and the injector of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring to  FIG. 2 , an exemplary embodiment of the injector  10  of the present disclosure include an injector plunger  12  having a nozzle valve assembly  16  and injector plunger  12  that provides improved spray distribution, reduced nozzle cavitation, lower end of injection variation, and a faster injection rate shape. The plunger  12 , also referred to as a needle or nozzle valve element, is mounted for reciprocal movement in nozzle assembly  16  between a closed position in abutment against a plunger seat  18  to block fuel flow through injector orifices  20  formed a nozzle housing  28  and an open position positioned a spaced distance from plunger seat  18  to permit fuel flow through injector orifices  20 . As explained below, plunger  12  includes two balanced restriction or gain orifices  40 ,  42  for improved fueling control. In an exemplary embodiment, the orifices  40 ,  42  are formed in an upper guide  22  of plunger  12  positioned in, and at one end of, nozzle assembly  16 . 
         [0015]    The annular radially protruding upper guide  22  is positioned at one end of an annular lower supply chamber  24  formed in the nozzle valve assembly  16  upstream of a lower guide  14  positioned in nozzle valve assembly  16  closely adjacent plunger seat  18 . The lower supply chamber  24  is positioned longitudinally between the upper guide  22  and the lower guide  14  and includes an axial extent or length greater than an axial extent of the upper guide  22 , and a radial width at least as wide as the radial width of the upper guide  22  resulting in a lower supply chamber  24  having a larger volume than other fuel passages located between upper guide  22  and lower guide  14 . Both the upper guide  22  and the lower guide  14  are formed in, preferably, a one-piece nozzle housing  28  when the plunger  12  is assembled in the injector  10 . The upper guide  22  is positioned adjacent an outer end of the nozzle housing  28  and includes an outer annular surface or extent  29  sized and positioned to form a close sliding fit with the inner wall or surface of the nozzle housing  28  to create a substantial fluid seal while permitting unhindered reciprocal movement. The lower guide  14  is positioned in a lower bore  26  having an outer diameter less than the outer diameter of the lower supply chamber  24 . As shown in  FIGS. 2 and 3 , the lower guide  14  includes elongated guiding flutes  30  extending radially outwardly to form respective outer annular surfaces sized and positioned to form a close sliding fit with the inner wall of the nozzle housing  28  forming the lower bore  26 , and axial passages  32  positioned between the flutes to connect the lower bore  26  above and below lower guide  14  permitting passage of fuel through lower guide  14 . Preferably, axial passages  32  are sized to avoid any restriction in the fuel flow through guide  14  thereby permitting unrestricted fuel flow to injector orifices  20 . The lower guide  14  is positioned axially along the lower bore  26  closer to the plunger or nozzle seat  18  than to the lower supply chamber  24 . Therefore a greater longitudinal or axial portion of lower bore  26  is positioned above lower guide  14  than below lower guide  14 . Also, the lower supply chamber  24  is positioned longitudinally/axially between upper guide  22  and upper end of lower bore  26  to receive fuel from restriction orifices  40 ,  42  and deliver fuel to the annular fuel passage positioned in lower bore  26  radially between the inner wall of nozzle housing  28  and the outer surface of injector plunger  12 . In addition, the axial distance along the longitudinal axis  15  between upper guide  22  and lower guide  14  is at least twice the axial distance between lower guide  14  and valve seat  18   
         [0016]    The plunger  12  further includes two flow passages  34 ,  36  formed in the upper guide  22  to connect an upper supply chamber  38  to the lower supply chamber  24 . A respective gain orifice  40 ,  42 , having a smaller cross-sectional flow area than the respective flow passage, is formed in each flow passage  34 ,  36  to restrict the flow of fuel from the upper supply chamber  38  to the lower supply chamber  24  to create a desired force profile on the plunger  12 . The general operation of an inner restriction passage is discussed in U.S. Pat. No. 6,499,467, the entire contents of which is hereby incorporated by reference. The injector of U.S. Pat. No. 6,499,467 is also shown in  FIG. 1 , and represents the standard injector/plunger used as a comparison in the discussion, charts and graphs herein. Also, the upper portion of injector  10  not shown in  FIG. 2  may be the same as the upper portion of the injector disclosed in U.S. Pat. No. 6,499,467. 
         [0017]    As shown in  FIG. 2 , the passages  34 ,  36  and thus the orifices  40 ,  42  are symmetrically oriented in the injector plunger  12  to enhance plunger guiding, flow balance, and fuel control. In one exemplary embodiment, shown in  FIG. 2 , each passage  34 ,  36  may include a first angled passage  44 ,  46  extending downwardly from the upper supply chamber  38  and inwardly at an angle toward the longitudinal axis  15  of plunger  12  and a second angled passage  48 ,  50  connected with the first angled passage  44 ,  46 , respectively, and extending outwardly and downwardly to connect with the lower supply chamber  24 . In this first exemplary embodiment, the second angled passages  48 ,  50  form the orifices  40 ,  42 , and the passages and orifices are all positioned in a common plane extending through the injector axis. Alternatively, the orifices may be formed along passages  48 ,  50 . In another exemplary embodiment, shown in  FIGS. 4   a  and  4   b , each flow passage is formed by a single linear passage  52 ,  54  extending through the upper guide  22  and having a central axis  56  positioned in a plane parallel to the longitudinal axis  15  of plunger  12 . Passages  52 ,  54  are positioned at an angle from the plunger axis  15  to connect the upper supply chamber  38  to the lower supply chamber  24 . In the exemplary embodiments, lower supply chamber  24  is sized and positioned to provide an increased volume downstream of the gain orifices  40 ,  42  compared to conventional injectors. 
         [0018]    An unexpected benefit of the plunger  12  and injector  10  is improved shot-to-shot EOI (end of injection) variation, resulting from the improved guiding and alignment. Another unexpected benefit of this design is a faster injection rate at the start of injection due to more volume downstream of the gain orifices  40 ,  42  (larger lower supply chamber  24 ), in addition to the improved guiding and alignment of the plunger  12 . This benefit may also be due to less pressure reduction downstream of the gain orifices  40 ,  42  when the plunger lifts. 
         [0019]    The balanced and guided plunger  12  has the following improvements: 
         [0000]    1. Structural symmetry: The dual gain orifices  40 ,  42  are symmetrically positioned to advantageously eliminate bending in the injector plunger. Conventional designs using a single, or asymmetrical, inner restriction orifice, result in bending of the plunger around the notch when the injector is pressurized with fuel and the lower plunger is loaded, thereby undesirably creating eccentricity between the plunger tip and nozzle seat.
 
2. Hydraulic symmetry: The dual gain orifices  40 ,  42  balance the flow so there is not a hydraulic side force generated that pushes the plunger eccentrically when the plunger is lifted. The symmetrical positioning of the gain orifices allows fluid pressure and flow forces in one orifice/passage on one side of the plunger to be counteracted by fluid pressure and flow forces in the other orifice/passage on the other side of the plunger. As a result, the plunger reciprocates in a more linear manner along the desired longitudinal axis.
 
3. Improved guiding: At least the following features maintain the plunger tip centered on the nozzle seat  18  when the plunger lifts.
 
         [0020]    a. The upper  22  and lower  14  guides are spaced far apart in the nozzle housing  28 . 
         [0021]    b. The lower guide  14  is close to the nozzle seat  18 . 
         [0022]    c. The lower diameter guide is less subject to increased clearance when the nozzle housing  28  is pressurized and therefore provides improved guiding under pressure. 
         [0023]    Calculations at 2600 bar indicate a 8 mm ID of the upper nozzle bore dilates 0.024 mm diametrically, whereas a 4 mm ID of the lower nozzle bore only dilates 0.010 mm diametrically. Optional machining of the gain orifices  40 ,  42  may also be used to provide through hole drilling for improved machining and less chance of burrs in drilling intersections. The improved guiding is evident by comparing the spray visualization photos of  FIGS. 5   a  and  5   b .  FIG. 5   a  shows the injector spray distribution near the start of injection, which is when the plunger is just starting to lift, for a conventional injector, such as shown in  FIG. 1 , while  FIG. 5   b  shows a more balanced and deeper/extended spray distribution near the start of injection for injector  10  including the present balanced and guided plunger  12 . 
         [0024]    The balanced and guided plunger  12  also results in improved shot to shot EOI variation.  FIGS. 6   a  and  6   b  are graphs showing test data comparing the EOI variation of a conventional injector with the injector  10  including the balanced and guided plunger  12  consistent with the present disclosure, respectively. 
         [0025]    Another unexpected improvement has been a faster injection rate at the start of injection. The faster injection rate may be due to more volume downstream of the gain orifice as provided by the enlarged lower supply chamber, and also the improved guiding and alignment of the plunger. This benefit may also be due to less pressure reduction downstream of the gain orifices when the plunger lifts. CFD modeling with a centered plunger showed no spray hole cavitation. The CFD results have been confirmed with improvement in spray hole cavitation in several cavitation rig tests when comparing the conventional plungers with the present balanced and guided plunger  12 . 
         [0026]    While various embodiments in accordance with the present disclosure have been shown and described, it is understood that the disclosure is not limited thereto. The present disclosure may be changed, modified and further applied by those skilled in the art. Therefore, this disclosure is not limited to the detail shown and described previously, but also includes all such changes and modifications.