Patent Publication Number: US-2021164425-A1

Title: Single-fluid common rail fuel injector with fuel recovery fitting and engine system using same

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a common rail fuel system in an internal combustion engine, and more particularly to single-fluid common rail fuel injector assembly having a fuel recovery fitting. 
     BACKGROUND 
     Modern fuel systems used in internal combustion engines are typically relatively complex and highly sophisticated apparatus having many moving parts, and are required to handle high absolute pressures, as well as rapid pressure swings during operation. Engineers have discovered that precise control over fuel injection characteristics, including injection pressure, injection timing, injection rate shape, and other factors can have beneficial impacts on engine emissions. For example, it has been observed that a small pilot injection followed by a subsequent main injection can assist in promoting relatively rapid and complete combustion of a fuel charge in an engine cycle. Post injections, where a small injection follows a larger main injection, can also have beneficial impacts in certain circumstances. Fuel injection rate shape, referring to the shape of a signal trace reflecting fuel injection rate, can also be varied amongst square, ramp, and other shapes, to varying effect. 
     The implementation and control of pilot injections, post injections, rate shapes, and other fuel injection properties can differ based upon the basic design of fuel injectors and fuel systems. Where mechanical actuation of a fuel injector is employed, spill valves that selectively open to spill pressure during a plunger pressurization event in a fuel injector are commonly used to provide desired fuel injection characteristics. In other fuel systems, for example, common rail fuel systems where pressurized fuel is continuously available within a fuel injector, different strategies are used to control or vary injection properties. In the context of common rail fuel systems, success in rate shaping has been elusive, required unduly complex fuel injector designs, an injector actuation fluid different from the fuel that is injected, or presented still other challenges. U.S. Pat. No. 7,111,614 to Coldren et al. is directed to a known single-fluid injector apparently having rate shaping capability. 
     SUMMARY OF THE INVENTION 
     In one aspect, an internal combustion engine system includes an engine head having formed therein a plurality of fuel injector bores, a fuel supply including a pressurized fuel supply conduit, and a fuel return conduit fluidly connected to the fuel supply. The engine system further includes a plurality of fuel injectors positioned in the plurality of fuel injector bores. Each of the plurality of fuel injectors has formed therein an actuation fuel supply passage fluidly connected to the pressurized fuel supply conduit, a pressure control passage, a plunger control passage, a nozzle fuel supply passage extending between a plunger cavity and a nozzle outlet, and at least one actuation fuel outlet. Each of the plurality of fuel injectors further includes an intensifier plunger, a nozzle check, an injection control valve, and an intensifier control valve. A plurality of fuel recovery fittings are coupled to the plurality of fuel injectors and each fluidly connects the at least one actuation fuel outlet in the respective fuel injector to the fuel return conduit. 
     In another aspect, a fuel injector assembly includes an injector housing having formed therein an actuation fuel supply passage, a pressure control passage, an intensifier passage, a nozzle fuel supply passage extending between a plunger cavity and a nozzle outlet, and at least one actuation fuel outlet. The fuel injector assembly further includes an intensifier plunger having an actuation surface exposed to the intensifier passage, and a pressurization surface exposed to the plunger cavity. The fuel injector assembly also includes a nozzle check movable between a closed check position blocking the nozzle outlet, and an open check position, and having a closing hydraulic surface exposed to a fluid pressure of the pressure control passage. An injection control valve is movable between a first control valve position, where the pressure control passage is fluidly connected to the actuation fuel supply passage, and a second control valve position, where the pressure control passage is blocked from the actuation fuel supply passage and fluidly connected to the at least one actuation fuel outlet. The fuel injector assembly further includes an intensifier control valve, and a fuel recovery fitting, having a recovered fuel outlet coupled to the injector housing and fluidly connecting the at least one actuation fuel outlet to the recovered fuel outlet. 
     In still another aspect, a method of operating a common rail fuel system in an internal combustion engine includes moving a control valve in a fuel injector between a first control valve position and a second control valve position to vary a pressure of fuel in a pressure control passage in the fuel injector. The method further includes opening a nozzle check in the fuel injector based on a reduction in the pressure of fuel in the pressure control passage caused by the moving of the control valve, and varying a flow of fuel to a spool valve in the fuel injector based on the varying of the pressure of fuel in the pressure control passage. The method still further includes varying a rate of advancement of an intensifier plunger through a plunger cavity in the fuel injector based on the varied flow of fuel through the spool valve, and injecting fuel from the plunger cavity through a nozzle outlet in the fuel injector opened by the opening of the nozzle check at a fuel injection rate having a rate shape that is based on the varied rate of advancement of the intensifier plunger. The method still further includes recovering fuel from at least one actuation fuel outlet of the fuel injector in a fuel recovery fitting coupled with the fuel injector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of an engine system, according to one embodiment; 
         FIG. 2  is a sectioned side diagrammatic view of a fuel injector assembly, according to one embodiment; 
         FIG. 3  is a sectioned side diagrammatic view of a portion of the engine system of  FIG. 1 ; 
         FIG. 4  is a side diagrammatic view of a fuel recovery fitting, according to one embodiment; and 
         FIG. 5  is a rate trace showing example fuel injection rate shaping characteristics, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown an internal combustion engine system  10  according to one embodiment. Internal combustion engine system  10  (hereinafter “engine system  10 ”) includes an engine  12  having a cylinder block  14  with a plurality of cylinders  16  formed therein. Engine  12  can include a compression-ignition diesel engine, however, the present disclosure is not thereby limited. Engine  12  further includes an engine head  18  coupled to cylinder block  14  and having formed therein a plurality of fuel injector bores  20 . A fuel system  21  is coupled to engine  12  and includes a fuel supply  22  having a pressurized fuel supply conduit  24 . Pressurized fuel supply conduit  24  can include a higher pressure fuel supply conduit, and fuel system  21  also includes a lower pressure fuel supply conduit  26 , and a still lower pressure fuel return conduit  28  fluidly connected to fuel supply  22 . Fuel system  21  also includes a fuel tank  30 , a fuel filter  32 , and a fuel transfer pump  34  structured to supply fuel having passed through filter  32  to a fuel pressurization pump  36 . 
     Fuel pressurization pump  36  could include an inlet-metered pump, an outlet-metered pump, or still another type of pump structured to pressurize fuel for actuating components in fuel system  21  and providing fuel for injection, as further discussed herein. In the illustrated embodiment fuel pressurization pump  36  includes a higher pressure outlet  38  and a lower pressure outlet  40  structured to feed fuel to fuel supply conduit  24  and fuel supply conduit  26 , respectively. One or more additional fuel filters  42  may be positioned fluidly between fuel pressurization pump  38  and engine head  18 , for example in fuel supply conduit  26 . Also in the illustrated embodiment fuel supply conduit  24  and fuel supply conduit  26  feed fuel through cylinder block  14  by way of passages and/or connectors located in cylinder block  14  and/or engine head  18 . Fuel supply conduit  24  can be understood as a common rail. Common rail is intended herein to refer to any of a number of different fuel containment and supply strategies where a single pressurized fuel reservoir is employed to maintain fuel at a desired pressure for supplying to multiple different fuel injectors. Fuel supply conduit  24  may be maintained at a lower pressure than in other common rail systems, as pressurization to an injection pressure takes place within fuel injectors as further discussed herein. Quill connectors, pressure sensors, relief valves, or other known pressurized fuel supply connections and monitoring or control hardware may be provided in engine system  10 , as will be understood to those skilled in the art. 
     A valve cover  44  is also attached to engine head  18 , such that a space  46  is formed between valve cover  44  and engine head  18 . Engine system  10 , and fuel system  21 , also includes a plurality of fuel injectors  50  in a plurality of fuel injector assemblies  52  positioned in the plurality of fuel injector bores  20 . Fuel injector assemblies  52  each also include a fuel recovery fitting  54  coupled to the corresponding one of the plurality of fuel injectors  50 . A plurality of fuel seals  142  are formed between the plurality of fuel recovery fittings  54  and the respective fuel injectors  50 , and also potentially between fuel recovery fittings  54  and engine head  18  as further discussed herein. Each of the plurality of fuel recovery fittings  54  may be positioned at least partially within space  46 . Engine oil supplied directly or incidentally into space  46  could contact fuel recovery fittings  54  to assist in cooling. 
     Referring also now to  FIG. 2 , there are shown features of one of fuel injector assemblies  52 , hereinafter referred to in the singular, in greater detail. Fuel injector assembly  52  includes fuel injector  50  and fuel recovery fitting  54  as noted above. Fuel injector  50  also includes an injector housing  56  having formed therein an actuation fuel supply passage  58 , a pressure control passage  60 , an intensifier passage  62 , a nozzle fuel supply passage  64  extending between a plunger cavity  65  and a nozzle outlet  66 , and at least one actuation fuel outlet  68  and  70 . Injector housing  56  includes a number of different injector housing components and, in the illustrated embodiment, an injector body  57  coupled to a casing  59 , for example by way of a threaded connection. Injector body  57  can be screwed into casing  59  to clamp together components in injector housing  56  in a generally known manner. The at least one actuation fuel outlet can include a drain port  68 , and a fuel leakage path  70 . Fuel injector  50  also includes an intensifier plunger  72  having an actuation surface  74  exposed to intensifier passage  62 , and a pressurization surface  76  exposed to plunger cavity  65 . A nozzle check  78  is movable within injector housing  56  between a closed check position blocking nozzle outlet  66 , and an open check position at which nozzle outlet  66  is not blocked. Nozzle check  78  may be directly controlled and includes a closing hydraulic surface  80  exposed to a fluid (fuel) pressure of pressure control passage  60 . Fuel injector  50  also includes an injection control valve  82  movable between a first control valve position, where pressure control passage  60  is fluidly connected to actuation fuel supply passage  58 , and a second control valve position, where pressure control passage  60  is blocked from actuation fuel supply passage  58 . At the second control valve position pressure control passage  60  is fluidly connected to the at least one actuation fuel outlet, namely, drain port  68 . 
     Injection control valve  82  may be part of a control valve subassembly  118  including a valve body  120  and a valve member, such as a poppet valve member  122 , movable relative to valve body  120  to contact a lower seat  124  or an upper seat  126  at the first control valve position and the second control valve position, respectively. A biaser  128 , such as a conventional biasing spring, biases valve member  122  toward the second control valve position. An electrical actuator  130 , such as a solenoid electrical actuator, is provided and can be varied in electrical energy state to move valve member  122  in opposition to a bias of biaser  128  from the first control valve position to the second control valve position. 
     Fuel injector  50  also includes an intensifier control valve  86 . In a practical implementation strategy, intensifier control valve  86  includes a spool valve having a first end surface  88  and a second end surface  90 . First end surface  88  can be exposed to a fluid pressure of pressure control passage  60 , and second end surface  90  can be exposed to a fluid pressure of actuation fuel supply passage  58 . By varying a position of injection control valve  82 , fluid connections amongst pressure control passage  60 , actuation fuel supply passage  58 , and drain port  68  can be varied. Lower seat  124  may be a three-way valve seat formed in injector housing  56  and positioned fluidly amongst pressure control passage  60 , actuation fuel supply passage  58 , and drain port  68 . Thus, injection control valve  82 , namely, valve member  122 , blocks three-way valve seat  124  at the first control valve position, and does not block valve seat  124  at the second control valve position. 
     Those skilled in the art will be familiar with certain related aspects of functionality of a pilot control valve, such as injection control valve  82 , and a slide-type hydraulic valve, such as intensifier control valve  86 . During, or in preparation for, a fuel injection event, injection control valve  82  can be opened and closed multiple times to vary a pressure acting upon first end surface  88  by way of varied pressure in pressure control passage  60 . When a fuel pressure of actuation fuel supply passage  58  is acting on both end surface  88  and end surface  90  of intensifier control valve  86 , intensifier control valve  86  may be balanced, and positioned such that intensifier control passage  62  is at a lower pressure, such as a drain pressure, and such that intensifier plunger  72  is retracted, approximately as shown in  FIG. 2 . When first end surface  88  is exposed to a lower fluid pressure, such as where injection control valve  82  is actuated open, the higher fuel pressure prevailing in actuation fuel supply passage  58  can cause intensifier control valve  86  to move, upward in the  FIG. 2  illustration, to provide high pressure flow through and/or around intensifier control valve  86  to increase pressure of and provide a flow of fuel into intensifier control passage  62 . As a result, intensifier plunger  72  can advance, downward in the  FIG. 2  illustration, through plunger cavity  65 . By exploiting the aforementioned opening and closing of injection control valve  82  in anticipation of, or during, a fuel injection event, the rate of advancement of intensifier plunger  72  through plunger cavity  65  can be varied to vary injection rate shape as further discussed herein. It will thus be understood that injection control valve  82  may be thought of as controlling multiple hydraulic fuel circuits by moving between lower seat  124  and upper seat  126 . As also shown in the illustrated embodiment, injector housing  56  further has formed therein an actuation fuel inlet  61  fluidly connected to fuel supply conduit  24  within engine head  18 . Injector housing  56  also includes a nozzle fuel inlet  63 , separate from actuation fuel inlet  61 , and fluidly connected to nozzle fuel supply passage  64 , and to fuel supply conduit  26  within engine head  18 . 
       FIG. 3  also shows additional features of fuel recovery fitting  54 . Fuel recovery fitting  54  may be coaxially arranged with injector housing  56 . Injector housing  56  defines a longitudinal injector axis  100 , and fuel recovery fitting  54  defines a longitudinal fitting axis  104 . The axes  100  and  104  are shown co-linear in the drawings. Fuel recovery fitting  54  also includes a sleeve portion  106  that is coaxially arranged with injector housing  56 . Sleeve portion  106  includes an inside surface  108 . Fuel recovery fitting  54  also includes a projecting side tube  116  having a recovered fuel outlet  102  formed therein. Recovered fuel outlet  102  may fluidly connect to fuel return conduit  28 . Accordingly, the plurality of fuel recovery fittings  54  may fluidly connect in parallel to fuel return conduit  28 . Fuel return conduit  28  may feed recovered fuel from actuating injection control valve  82 , to fuel tank  30 . In  FIG. 1  the location of returning recovered fuel to fuel supply  22  by way of fuel return conduit  28  is upstream of fuel tank  30 . In another embodiment, fuel return conduit  28  could connect to an inlet to transfer pump  34 , or potentially to an inlet to fuel pressurization pump  36 . It is contemplated that some fuel pressure may be maintained in fuel recovery fitting  54  that is greater than atmospheric pressure. Accordingly, an efficiency gain may be realized in that fuel, having already been filtered, can be supplied to fuel pressurization pump  36  at a slightly elevated pressure than were the fuel supplied directly from fuel tank  30 , which will typically be at atmospheric pressure. 
     It will be recalled that injection control valve  82  may be part of a control valve subassembly  118 . Control valve subassembly  118  may have an outside surface  119 , and a fuel collection cavity  121  extends between inside surface  108  of sleeve portion  106  and outside surface  119  of control valve subassembly  118 . It will also be recalled the at least one actuation fuel outlet can include drain port  68  and also leakage path  70 . During moving valve member  122  some pressurized fuel can be expected to leak through a clearance between valve body  120  and valve member  122 , and find its way outside of injector housing  56 . Fuel collection cavity  121  is simultaneously fluidly connected with leakage path  70  and drain port  68 . Continued expelling of pressurized fuel into fuel collection cavity  121  can be expected to assist in maintaining a flow of fuel from the respective fuel recovery fitting  54  of each fuel injector  50  to fuel return conduit  28 . The flow of fuel can also assist in cooling control valve subassembly  118 . Fuel seal  142  may fluidly seal amongst engine head  18 , fuel injector  50 , and fuel recovery fitting  54 . In the illustrated embodiment, injector body  57  has plunger cavity  65  formed therein, and fuel seal  142  fluidly seals between fuel recovery fitting  54  and injector body  57 . In particular, fuel recovery fitting  54  includes a radially projecting flange  140 , and fuel seal  142  may seal with flange  140  and with fuel injector  50 , including injector body  57 , and with engine head  18 . 
     Referring also now to  FIG. 4 , there are shown some additional features of fuel recovery fitting  54 . Fuel recovery fitting  54  has a first axial end  112  and a second axial end  114 , with projecting side tube  116  being positioned adjacent to second axial end  114 . Second axial end  114  includes flange  140 . First axial end  112  may include an opening  111  formed therein for accommodating electrical connections for electrical actuator  130 , and fluidly sealed with injector housing  56  around opening  111 . In one implementation, fuel recovery fitting  54  can be threadedly engaged with fuel injector  50 , such as by threaded engagement with injector body  57 . In other instances, fuel recovery fitting  54  might be attached by some other mechanism to fuel injector  50 , for example a snap-fit or other interference fit, or potentially attached to engine head  18 . Fuel recovery fitting  54  further includes an outer diameter dimension  150 , an axial length dimension  155 , and a flange outer diameter dimension  159 . An outer surface  110  of fuel recovery fitting  54  may be substantially cylindrical and extends circumferentially around longitudinal fitting axis  104 . Flange  140  may also be shaped so as to extend radially outward from sleeve portion  106 , and having an outer perimeter defining a circle centered on fitting longitudinal axis  104 . Axial length dimension  155  may be greater than outer diameter dimension  150 , such as by a factor of 2-3, or more. Axial length dimension  155  may also be greater than flange outer diameter dimension  159 , for example 1.5 times greater, or more. Side tube  116  may extend generally perpendicular to axis  104  to a location that is radially outward of flange  140 . 
     INDUSTRIAL APPLICABILITY 
     Referring to the drawings generally, operating fuel system  31  in engine system  10  can include moving control valve  82  between its first control valve position and second control valve position, to vary a pressure of fuel in pressure control passage  60  as discussed herein. Nozzle check  78  is opened based on a reduction in the pressure of fuel in pressure control passage  60  caused by the moving of control valve  82 . As discussed above, intensifier control valve  86  is adjusted to vary a flow of fuel therethrough based on the varying of the pressure of fuel in pressure control passage  60 . As also discussed herein, a rate of advancement of intensifier plunger  72  through plunger cavity  63  is varied based on the varied flow of fuel through intensifier control valve  86 . With nozzle check  78  opened, fuel from plunger cavity  65  is injected through nozzle outlet  66  at a fuel injection rate having a rate shape that is based on the varied rate of advancement of intensifier plunger  72 . 
     Embodiments are contemplated where injection control valve  82  is moved multiple times to open and close seat  124 , with intensifier control valve  86  correspondingly accelerated, decelerated, reversed, stopped, or fully opened and then fully closed, all during, or in anticipation of, a single injection cycle. Accordingly, pressure and flow of fuel in intensifier passage  62  can be varied in a manner that produces numerous different fuel injection rate shapes. The fuel leaked through leakage path  70 , and fuel expelled through drain port  68 , is recovered by way of fuel recovery fitting  54  in fuel collection cavity  108 , and returned to fuel supply  22  as discussed herein. 
     Referring now to  FIG. 5 , there is shown a graph  200  illustrating example rate shaping that can be produced in a fuel injection, according to the present disclosure. A first trace is shown at  210 , and illustrates an example ascending ramp shape in a main fuel injection  240 . A second trace is shown at  220  and illustrates a different ascending ramp shape that might be produced in main injection  240 . An area between trace  210  and trace  220 , between a time t 2  and a time t 3 , represents rate shapes that could be varied essentially infinitely using fuel system  21 . At a time t 4 , trace  210  drops towards zero, illustrating fuel injection cut-off. Trace  220  drops back towards zero at approximately a time t 5 . Again, a timing, and potentially a shape, of end of injection rate could be varied between the shapes of trace  210  and trace  220  essentially infinitely. A pilot injection  230  is shown at about a time t 1  by way of reference number  230 . In addition to the pilot shot, ascending ramp rate shape, and injection cut-off variations shown in  FIG. 5 , post injections, square injections, multiple pilot shots, multiple post shots, and still other flexibility is anticipated in view of the present disclosure. It will also be appreciated that this flexibility in rate shaping using fuel system  21  is possible in a single-fluid injector, using fuel for both injection and actuation. Such capabilities contrast from other strategies where pressurized engine oil, or another fluid, is used for actuation while fuel itself is injected. 
     The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims. As used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.