Patent Publication Number: US-7591247-B2

Title: Fuel injector

Description:
TECHNICAL FIELD 
   The present disclosure is directed to a fuel injector and, more particularly, to a fuel injector having a backup leak limiter. 
   BACKGROUND 
   Common rail fuel systems typically employ multiple closed-nozzle fuel injectors to inject high pressure fuel into the combustion chambers of an engine. Each of these fuel injectors may include a nozzle assembly having a cylindrical bore with a nozzle supply passageway and a nozzle outlet. A needle check valve may be reciprocatingly disposed within the cylindrical bore and biased toward a closed position where the nozzle outlet is blocked. In response to a deliberate injection request, the needle check valve may be selectively moved to open the nozzle outlet, thereby allowing high pressure fuel to flow from the nozzle supply passageway into the combustion chamber. 
   During operation of the fuel injector, it is possible for a tip portion of the nozzle to fail, leaving the nozzle continuously open. In order to ensure that the high pressure fuel is not continuously pumped into the combustion chamber, the common rail fuel system may employ a leak limiter to limit fuel leakage through the nozzle. One such device is described in U.S. Pat. No. 6,109,542 (the &#39;542 patent) issued to Morris et al. on Aug. 29, 2000. The &#39;542 patent describes a nozzle cavity housing a nozzle valve element, and a limiter valve disposed upstream of the nozzle cavity. The limiter valve is moved to an open position just prior to an intended injection to selectively communicate high pressure fuel with the nozzle cavity. Between desired injections of fuel into an associated combustion chamber, the limiter valve member is moved to a closed position to block communication of the high pressure fuel with the nozzle cavity. When the limiter valve member is in the closed position, only the fuel already in the nozzle cavity may leak into the combustion chamber upon failure of the nozzle tip. 
   Although the limiter valve of the &#39;542 patent may minimize the amount of fuel leakage from the nozzle cavity upon failure of the nozzle, it still allows all of the fuel already in the nozzle cavity to drain into the associated combustion chamber following each intended injection. This amount of fuel allowed to drain into the combustion chamber could still significantly affect engine performance, fuel consumption and emissions. 
   In addition, the limiter valve does not limit deliberate injections. In particular, even if the injector of the &#39;542 patent has experienced nozzle failure, the limiter valve of the &#39;542 patent will still move to the open position in response to a demand for injection. Under conditions of nozzle failure, even a deliberate injection could result in rough engine operation, poor fuel consumption, and increased emissions. 
   Further, the limiter valve of the &#39;542 patent may be complex, expensive, and increase unreliability in the common rail system employing the limiter valve. In particular, because the limiter valve is additive and performs no function other than leak limiting, the overall cost of the common rail system employing the limiter valve must increase. The additional components of the limiter valve also add to the overall complexity and the number of potential failure modes of the common rail system. 
   The fuel injector of the present disclosure solves one or more of the problems set forth above. 
   SUMMARY OF THE INVENTION 
   One aspect of the present disclosure is directed to a fuel injector. The fuel injector includes a nozzle member having a tip portion, at least one orifice disposed at the tip portion, a base portion, and a female conical seating surface disposed at the base portion. The fuel injector also includes a needle valve member slidingly disposed within the nozzle member and having a tip end configured to selectively restrict fuel flow through the at least one orifice, a base end, and a male conical seating surface disposed between the tip end and the base end. The male conical seating surface is configured to engage the female conical seating surface to restrict fuel flow through the at least one orifice and has a hydraulic surface area greater than a hydraulic surface area of the base end of the needle valve member. 
   Another aspect of the present disclosure is directed to a fuel injector. The fuel injector includes a nozzle member having a tip portion, at least one orifice disposed at the tip portion, a base portion, and a female conical seating surface disposed at the base portion. The fuel injector also includes a needle valve member slidingly disposed within the nozzle member and having a tip end configured to selectively restrict fuel flow through the at least one orifice, a base end, and a male conical seating surface disposed between the tip end and the base end. The male conical seating surface is configured to engage the female conical seating surface to restrict fuel flow through the at least one orifice, and has a cone angle greater than a cone angle of the female conical seating surface. 
   Yet another aspect of the present disclosure is directed to a method of operating a fuel injector. The method includes directing pressurized fuel to a nozzle member having at least one orifice at a tip end. The tip end has at least one female conical seating surface. The method further includes selectively moving a needle valve member having at least one male conical seating surface between a first position at which fuel is allowed to flow through the at least one orifice and a second position at which the male conical seating surface engages the female conical seating surface to restrict fuel flow through the at least one orifice. The method also includes engaging a second male conical seating surface of the needle valve member with a second female conical seating surface of the nozzle member to restrict fuel flow when the first male and female conical seating surfaces fail to engage. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic and diagrammatic illustration of an exemplary disclosed fuel system; 
       FIG. 2A  is a cross-sectional illustration of an exemplary disclosed fuel injector for the fuel system of  FIG. 1 ; and 
       FIG. 2B  is a cross-sectional illustration of a portion of the fuel injector shown in  FIG. 2A . 
   

   DETAILED DESCRIPTION 
   An exemplary embodiment of an engine  10  having a fuel system  12  is illustrated in  FIG. 1 . For the purposes of this disclosure, engine  10  is depicted and described as a four-stroke diesel engine. One skilled in the art will recognize, however, that engine  10  may be any other type of internal combustion engine such as, for example, a gasoline or a gaseous fuel-powered engine. Engine  10  may include an engine block  14  that defines a plurality of cylinders  16 , a piston  18  slidably disposed within each cylinder  16 , and a cylinder head  20  associated with each cylinder  16 . 
   Cylinder  16 , piston  18 , and cylinder head  20  may form a combustion chamber  22 . In the illustrated embodiment, engine  10  includes six combustion chambers  22 . However, it is contemplated that engine  10  may include a greater or lesser number of combustion chambers  22  and that combustion chambers  22  may be disposed in an “in-line” configuration, a “V” configuration, or any other suitable configuration. 
   As also shown in  FIG. 1 , engine  10  may include a crankshaft  24  that is rotatably disposed within engine block  14 . A connecting rod  26  may connect each piston  18  to crankshaft  24  so that a sliding motion of piston  18  within each respective cylinder  16  results in a rotation of crankshaft  24 . Similarly, a rotation of crankshaft  24  may result in a sliding motion of piston  18 . 
   Fuel system  12  includes components that cooperate to deliver injections of pressurized fuel into each combustion chamber  22 . Specifically, fuel system  12  may include a tank  28  configured to hold a supply of fuel, and a fuel pumping arrangement  30  configured to pressurize the fuel and direct the pressurized fuel to a plurality of fuel injectors  32  by way of a common manifold  34 . 
   Fuel pumping arrangement  30  may include one or more pumping devices that function to increase the pressure of the fuel and direct one or more pressurized streams of fuel to common manifold  34 . In one example, fuel pumping arrangement  30  includes a low pressure source  36  and a high pressure source  38  disposed in series and fluidly connected by way of a fuel line  40 . Low pressure source  36  may be a transfer pump configured to provide low pressure feed to high pressure source  38 . High pressure source  38  may be configured to receive the low pressure feed and to increase the pressure of the fuel to the range of about 40-190 MPa. High pressure source  38  may be connected to common manifold  34  by way of a fuel line  42 . A check valve  44  may be disposed within fuel line  42  to provide for one-directional flow of fuel from fuel pumping arrangement  30  to common manifold  34 . 
   One or both of low pressure and high pressure sources  36 ,  38  may be operably connected to engine  10  and driven by crankshaft  24 . Low and/or high pressure sources  36 ,  38  may be connected with crankshaft  24  in any manner readily apparent to one skilled in the art where a rotation of crankshaft  24  will result in a corresponding rotation of a pump drive shaft. For example, a pump driveshaft  46  of high pressure source  38  is shown in  FIG. 1  as being connected to crankshaft  24  through a gear train  48 . It is contemplated, however, that one or both of low and high pressure sources  36 ,  38  may alternatively be driven electrically, hydraulically, pneumatically, or in any other appropriate manner. 
   Fuel injectors  32  may be disposed within cylinder heads  20  and connected to common manifold  34  by way of a plurality of fuel lines  50 . Each fuel injector  32  may be operable to inject an amount of pressurized fuel into an associated combustion chamber  22  at predetermined timings, fuel pressures, and fuel flow rates. Fuel injectors  32  may be hydraulically, mechanically, electrically, or pneumatically operated. 
   The timing of fuel injection into combustion chamber  22  may be synchronized with the motion of piston  18 . For example, fuel may be injected as piston  18  nears a top-dead-center position in a compression stroke to allow for compression-ignited-combustion of the injected fuel. Alternatively, fuel may be injected as piston  18  begins the compression stroke heading towards a top-dead-center position for homogenous charge compression ignition operation. Fuel may also be injected as piston  18  is moving from a top-dead-center position towards a bottom-dead-center position during an expansion stroke for a late post injection to create a reducing atmosphere for aftertreatment regeneration. 
   As illustrated in  FIG. 2A , each fuel injector  32  may be a closed nozzle unit fuel injector. Specifically, each fuel injector  32  may include an nozzle case  52  housing a guide  54 , a nozzle member  56 , and a needle valve member  58 . 
   Nozzle case  52  may be a cylindrical member configured for assembly within cylinder head  20 . Nozzle case  52  may have a central space  60  for receiving guide  54  and nozzle member  56 , and an opening  62  through which a tip end  64  of nozzle member  56  may protrude. A sealing member such as, for example, an o-ring  66  may be disposed between guide  54  and nozzle member  56  to restrict fuel leakage from fuel injector  32 . 
   Guide  54  may also be a cylindrical member having a central space  68  configured to receive needle valve member  58 . One or more fuel supply passageways  70  may be included within guide  54  to allow communication of pressurized fuel from fuel line  50  with nozzle member  56 . 
   Nozzle member  56  may likewise embody a cylindrical member having a central space  72  that is configured to receive needle valve member  58 . In particular, nozzle member  56  may include a first female conical seating surface  74  located at tip end  64 , and a second female conical seating surface  76  located at a base end  78 . As illustrated in  FIG. 2B , second female conical seating surface  76  may have a cone angle θ 1 . One or more orifices  80  seen in  FIG. 2A  may be located at tip end  64  to allow injection of pressurized fuel from central space  72  into combustion chamber  22 . 
   Needle valve member  58  may be an elongated cylindrical member that is slidingly disposed within housing guide  54  and nozzle member  56 . Needle valve member  58  may be movable between a first position at which a tip end  82  of needle valve member  58  restricts a flow of fuel through orifices  80 , and a second position at which orifices  80  are unobstructed to allow fuel flow into combustion chamber  22 . Needle valve member  58  may include a first male conical seating surface  84  and a second male conical seating surface  86 . First male conical seating surface  84  may be configured to seat against first female conical seating surface  74  of nozzle member  56 , while second male conical seating surface  86  may be configured to seat against second female conical seating surface  76 . As illustrated in  FIG. 2B , second male conical seating surface  86  may have a cone angle θ 2 , which is greater than θ 1 . When first male conical seating surface  84  of needle valve member  58  is engaged with first female conical seating surface  74  of nozzle member  56  (referring to  FIG. 2A ), second male and female conical seating surfaces  86 ,  76  are not engaged. The “d”, illustrated in  FIG. 2B , may be representative of the vertical distance between an outer periphery  88  of second male conical seating surface  86  and second female conical seating surface  76  when first male and female conical surfaces  84 ,  74  are engaged and needle valve member  58  is in the first position. 
   Needle valve member  58  may be normally biased toward the first position. In particular, as seen in  FIG. 2A , each fuel injector  32  may include a spring  90  disposed between a stop  92  of guide  54  and a seating surface  94  of needle valve member  58  to axially bias tip end  82  toward orifices  80 . The difference between the uncompressed length of spring  90  and the compressed length when needle valve member  58  is in the first position may be greater than the distance “d”. Alternatively, it is contemplated that the difference between the uncompressed length of spring  90  and the compressed length when needle valve member  58  is in the first position may not be greater than the distance “d”. A first spacer  96  may be disposed between spring  90  and stop  92 , and a second spacer  98  may be disposed between spring  90  and seating surface  94  to reduce wear of the components within fuel injector  32 . 
   Needle valve member  58  may have multiple driving hydraulic surfaces. In particular, needle valve member  58  may include a base end having a hydraulic surface  100  tending to drive needle valve member  58  toward the first or closed position when acted upon by pressurized fuel, and a hydraulic surface  104  that tends to oppose the bias of spring  90  and drive needle valve member  58  in the opposite direction toward the second or open position. The area of hydraulic surface  104  may be less than a hydraulic surface area defined by outer periphery  88 . In one example, the area of hydraulic surface  104  may be less than one half of the hydraulic surface area defined by outer periphery  88 . 
   An actuator  106  may be disposed opposite tip end  82  of needle valve member  58  to initiate motion of needle valve member  58 . As described earlier, fuel injectors  32  illustrated in  FIGS. 2A and 2B  are hydraulically driven. In particular, actuator  106  may selectively communicate hydraulic surface  100  either with high pressure fuel from fuel supply passageways  70  or with a drain line (not shown) that leads to tank  28  (referring to  FIG. 1 ). This selective communication may create force imbalances that move needle valve member  58  between the first or closed position and the second or open position. Operation of actuator  106  will be described in more detail below. 
   INDUSTRIAL APPLICABILITY 
   The fuel injector of the present disclosure has wide applications in a variety of engine types including, for example, diesel engines, gasoline engines, and gaseous fuel-powered engines. The disclosed injector may be implemented into any engine that utilizes a pressurizing fuel system having closed orifice-type fuel injectors where limitation of fuel leakage into associated combustion chambers after nozzle tip failure is desired. The fuel leakage limiting operation of fuel injector  32  will now be explained. 
   Needle valve member  58  may be moved by an imbalance of force generated by fluid pressure. For example, when needle valve member  58  is in the first or closed position, pressurized fuel from fuel supply passageways  70  may act on hydraulic surface  100 . The force of spring  90  combined with the hydraulic force created at hydraulic surface  100  is greater than an opposing force created at hydraulic surface  104  thereby causing needle valve member  58  to remain in the first position, at which first male conical seating surface  84  engages first female conical seating surface  74  to restrict fuel flow through orifices  80 . To open orifices  80  and inject the pressurized fuel into combustion chamber  22 , actuator  106  may selectively drain the pressurized fuel from hydraulic surface  100 . This decrease in pressure acting on hydraulic surface  100  allows the opposing force acting upon hydraulic surface  104  to overcome the biasing force of spring  90 , thereby moving needle valve member  58  toward the open position. Similarly, to close and restrict fuel flow through orifices  80 , actuator  106  may selectively communicate the pressurized fuel from fuel supply passageways  70  with hydraulic surface  100 , thereby overcoming the force generated by hydraulic surface  104  and causing needle valve member  58  to move with the bias of spring  90  toward the first position. 
   Over time, tip end  64  of nozzle member  56  may erode, deteriorate, and/or break away, leaving tip end  64  open. The deterioration and/or breakage may be severe enough that needle valve member  58  may be unable to sufficiently restrict fuel flow through orifices  80  at tip end  64 . Without intervention, pressurized fuel may be allowed to spray unrestricted into combustion chamber  22  causing rough running of engine  10 , poor fuel consumption, and/or increased exhaust emissions. 
   Upon deterioration and/or breakage of tip end  64 , needle valve member  58  may descend past the first position and further into nozzle member  56 , until outer periphery  88  of second male conical seating surface  86  engages second female conical seating surface  76 . When outer periphery  88  of second male conical seating surface  86  engages second female conical seating surface  76 , tip end  64  and nozzle member  56  may be substantially isolated from pressurized fuel. The uncompressed length of spring  90  is selected to provide the additional movement of needle valve member  58  across the distance “d”. 
   The angle and outer periphery  88  of second male conical seating surface  86  provide leak limiting functions even during deliberate injections. In particular, because the cone angle θ 2  is greater than the cone angle θ 1 , it is ensured that outer periphery  88  of second male conical seating surface  86  engages and seals against second female conical seating surface  76 . Because outer periphery  88  defines a hydraulic surface area that is greater than the area of hydraulic surface  104 , the force generated across the surfaces of second spacer  98  and seating surface  94  when outer periphery  88  is sealed against second female conical seating surface  76 , in conjunction with the force of spring  90 , is great enough to overcome the force generated at hydraulic surface  104 , even when the pressurized fuel is drained from hydraulic surface  100  by actuator  106 . 
   Numerous advantages of fuel injector  32  may be realized over the fuel injectors of the prior art. In particular, because the leak limiting function of fuel injector  32  is performed by existing components of fuel injector  32 , namely existing needle valve member  58  and nozzle member  56 , the overall cost, complexity, and potential for failure of fuel system  12  employing fuel injector  32  is kept low. Further, because needle valve member  58  will continuously restrict fuel flow through nozzle member  56 , even during deliberate injections, the performance of engine  10 , fuel efficiency, and exhaust emissions may be improved. In addition, because needle valve member  58  restricts the flow of fuel through nozzle member  56 , rather than an upstream component, the amount of fuel allowed to leak from fuel injector  32  into combustion chamber  22  during nozzle tip failure may be minimized. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the fuel injector of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the injector disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and their equivalents.