Patent Publication Number: US-7588012-B2

Title: Fuel system having variable injection pressure

Description:
TECHNICAL FIELD 
   The present disclosure is directed to a fuel system and, more particularly, to a fuel system having variable injection pressure capabilities. 
   BACKGROUND 
   Common rail fuel injectors provide a way to introduce fuel into the combustion chambers of an engine. Typical common rail fuel injectors include an actuating solenoid that opens a fuel injector nozzle when the solenoid is energized. Fuel is then injected into the combustion chamber as a function of the time period during which the solenoid remains energized and the pressure of fuel supplied to the fuel injector nozzle. 
   To optimize engine performance and exhaust emissions, engine manufacturers may vary the pressure of the fuel supplied to the fuel injector nozzle. One such example is described in U.S. Patent Application Publication No. 2004/0168673 (the &#39;673 publication) by Shinogle published Sep. 2, 2004. The &#39;673 publication describes a fuel injection system having a fuel injector fluidly connectable to a first common rail and a second common rail. By fluidly connecting the fuel injector to the first common rail, fuel can be injected at a first pressure. By fluidly connecting the fuel injector to the second common rail, fuel can be injected at a second pressure that is independent of the first pressure. 
   Although the fuel injection system of the &#39;673 publication may adequately supply fuel to an engine at different pressures, it may be expensive. In particular, the two separate fluid rails and associated supply systems increase the number of components of the fuel injection system, which correspondingly increases the complexity and cost of the fuel injection system. 
   The fuel system 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 at least one orifice and a needle valve element with a tip end. The needle valve element is axially movable to selectively allow and block fuel flow through the at least one orifice with the tip end. The fuel injector also includes at least one supply passageway in communication with the tip end of the needle valve, and a variable restrictive device disposed within the at least one supply passageway. 
   Another aspect of the present disclosure is directed to a method of injecting fuel into a combustion chamber of an engine. The method includes directing pressurized fuel to at least one orifice of a nozzle member. The method also includes variably restricting the flow of pressurized fluid to the nozzle member to vary the pressure of the fuel injection. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic and diagrammatic illustration of an exemplary disclosed fuel system; 
       FIG. 2  is a schematic and cross-sectional illustration of an exemplary disclosed fuel injector for the fuel system of  FIG. 1 ; and 
       FIG. 3  is a graph depicting an exemplary operation of the fuel injector of  FIG. 2 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a work machine  5  having an engine  10  and an exemplary embodiment of a fuel system  12 . Work machine  5  may be a fixed or mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, power generation, transportation, or any other industry known in the art. For example, work machine  5  may embody an earth moving machine, a generator set, a pump, or any other suitable operation-performing work machine. 
   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 embody 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  may include 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 rail  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 rail  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 embody 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 30-300 MPa. High pressure source  38  may be connected to common rail  34  by way of a fuel line  42 . A check valve  44  may be disposed within fuel line  42  to provide for unidirectional flow of fuel from fuel pumping arrangement  30  to common rail  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 drivably 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 rail  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. 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. 2 , each fuel injector  32  may embody a closed nozzle unit fuel injector. Specifically, each fuel injector  32  may include an injector body  52  housing a guide  54 , a nozzle member  56 , a needle valve element  58 , a first solenoid actuator  60 , and a second solenoid actuator  62 . 
   Injector body  52  may be a generally cylindrical member configured for assembly within cylinder head  20 . Injector body  52  may have a central bore  64  for receiving guide  54  and nozzle member  56 , and an opening  66  through which a tip end  68  of nozzle member  56  may protrude. A sealing member such as, for example, an o-ring (not shown) may be disposed between guide  54  and nozzle member  56  to restrict fuel leakage from fuel injector  32 . 
   Guide  54  may also be a generally cylindrical member having a central bore  70  configured to receive needle valve element  58 , and a control chamber  72 . Central bore  70  may act as a pressure chamber, holding pressurized fuel continuously supplied by way of a fuel supply passageway  74 . During injection, the pressurized fuel from fuel line  50  may flow through fuel supply passageway  74  and central bore  70  to the tip end  68  of nozzle member  56 . 
   Control chamber  72  may be selectively drained of or supplied with pressurized fuel to control motion of needle valve element  58 . Specifically, a control passageway  76  may fluidly connect a port  78  associated with control chamber  72 , and first solenoid actuator  60 . Port  78  may be disposed within a side wall of control chamber  72  that is radially oriented relative to axial movement of needle valve element  58  or, alternatively, within an axial end portion of control chamber  72 . Control chamber  72  may be continuously supplied with pressurized fuel via a restricted supply passageway  80  that is in communication with fuel supply passageway  74 . The restriction of supply passageway  80  may allow for a pressure drop within control chamber  72  when control passageway  76  is drained of pressurized fuel. 
   Nozzle member  56  may likewise embody a generally cylindrical member having a central bore  82  that is configured to receive needle valve element  58 . Nozzle member  56  may further include one or more orifices  84  to allow injection of the pressurized fuel from central bore  82  into combustion chambers  22  of engine  10 . 
   Needle valve element  58  may be a generally elongated cylindrical member that is slidingly disposed within housing guide  54  and nozzle member  56 . Needle valve element  58  may be axially movable between a first position at which a tip end  86  of needle valve element  58  blocks a flow of fuel through orifices  84 , and a second position at which orifices  84  are open to allow a flow of pressurized fuel into combustion chamber  22 . 
   Needle valve element  58  may be normally biased toward the first position. In particular, each fuel injector  32  may include a spring  88  disposed between a stop  90  of guide  54  and a seating surface  92  of needle valve element  58  to axially bias tip end  86  toward the orifice-blocking position. A first spacer  94  may be disposed between spring  88  and stop  90 , and a second spacer  96  may be disposed between spring  88  and seating surface  92  to reduce wear of the components within fuel injector  32 . 
   Needle valve element  58  may have multiple driving hydraulic surfaces. In particular, needle valve element  58  may include a hydraulic surface  98  tending to drive needle valve element  58  toward the first or orifice-blocking position when acted upon by pressurized fuel, and a hydraulic surface  100  that tends to oppose the bias of spring  88  and drive needle valve element  58  in the opposite direction toward the second or orifice-opening position. 
   First solenoid actuator  60  may be disposed opposite tip end  86  of needle valve element  58  to control the opening motion of needle valve element  58 . In particular, first solenoid actuator  60  may include a two-position valve element disposed between control chamber  72  and tank  28 . The valve element may be spring-biased toward a closed position blocking fluid flow from control chamber  72  to tank  28 , and solenoid-actuated toward an open position at which fuel is allowed to flow from control chamber  72  to tank  28 . The valve element may be movable between the closed and open positions in response to an electric current applied to a coil associated with first solenoid actuator  60 . It is contemplated that the valve element may alternatively be hydraulically operated, mechanically operated, pneumatically operated, or operated in any other suitable manner. It is further contemplated that the valve element may alternatively embody a proportional type of valve element that is movable to any position between the closed and open positions. 
   Second solenoid actuator  62  may include a two-position valve element disposed between first solenoid actuator  60  and tank  28  to control a closing motion of needle valve element  58 . The valve element may be spring-biased toward an open position at which fuel is allowed to flow to tank  28 , and solenoid-actuated toward a closed position blocking fluid flow to tank  28 . The valve element may be movable between the open and closed positions in response to an electric current applied to a coil associated with second solenoid actuator  62 . It is contemplated that the valve element may alternatively be hydraulically operated, mechanically operated, pneumatically operated, or operated in any other suitable manner. It is further contemplated that the valve element may alternatively embody a three-position type of valve element, wherein bidirectional flows of pressurized fuel is facilitated. 
   As also illustrated in  FIG. 2 , a pressure control device  102  may be associated with each fuel injector  32 . Specifically, pressure control device  102  may include an actuator  104 , a variable restrictive device  106 , and a check valve  108 . Actuator  104  may be mechanically or hydraulically connected to variable restrictive device  106  by way of a communication link  110 , and to check valve  108  by way of a communication link  112 . 
   Actuator  104  may embody a piezo electric mechanism having one or more columns of piezo electric crystals. Piezo electric crystals are structures with random domain orientations. These random orientations are asymmetric arrangements of positive and negative ions that exhibit permanent dipole behavior. When an electric field is applied to the crystals, such as, for example, by the application of a current, the piezo electric crystals expand along the axis of the electric field as the domains line up. 
   Actuator  104  may be connected to mechanically or hydraulically control the motion of variable restrictive device  106  and check valve  108 . For example, as a current is applied to the piezo electric crystals of actuator  104 , actuator  104  may affect movement of variable restrictive device  106  via communication link  110  to decrease the restriction of pressurized fluid flowing to fuel injector  32 . Substantially simultaneously, actuator  104  may block check valve  108  in a flow blocking position via communication link  112 . In contrast, as the current is removed from the piezo electric crystals of actuator  104 , actuator  104  may move variable restrictive device  106  via communication link  110  to increase the restriction of pressurized fluid flowing to fuel injector  32 . Substantially simultaneously, actuator  104  may unblock check valve  108  via communication link  112 . It is contemplated that the piezo electric crystals of actuator  104  may be omitted, if desired, and the movement of variable restrictive device  106  and check valve  108  be controlled in another suitable manner. It is further contemplated that a single actuator  104  and/or a single variable restrictive device  106  may be associated with multiple fuel injectors  32  to reduce the number of components included within fuel system  12 . 
   Variable restrictive device  106  may be located within fuel line  50  or fuel supply passageway  74  to restrict the flow of pressurized fuel. For example, variable restrictive device  106  may include a proportional valve element or other suitable device movable by actuator  104  to restrict the flow of fuel to central bore  82  of nozzle member  56 . The amount of restriction may be dependent on the current applied to the piezo electric crystals of actuator  104 . This restriction of pressurized fuel may allow for a variable pressure of fuel with central bore  82 , resulting in a variable injection rate of fuel through orifices  84  and penetration depth into combustion chamber  22 . 
   Check valve  108  may be situated for unidirectional flow of fuel from fuel supply passageway  74  to tank  28 . Because the blocking or unblocking of check valve  108  is affected by the motion of actuator  104  and related to the restriction of variable restrictive device  106 , fuel flow through check valve  108  to tank  28  may only be permitted between injection events. In this manner, a substantially constant reference pressure may be maintained within central bore  82 . It is contemplated that check valve  108  may be omitted, if desired, and an additional 2-way type of valve alternatively included. 
     FIG. 3  illustrates an exemplary operation of fuel system  12 .  FIG. 3  will be discussed in the following section to further illustrate the disclosed system and its operation. 
   INDUSTRIAL APPLICABILITY 
   The fuel system of the present disclosure has wide application in a variety of engine types including, for example, diesel engines, gasoline engines, and gaseous fuel-powered engines. The disclosed fuel system may be implemented into any engine that utilizes a pressurizing fuel system wherein it may be advantageous to provide a variable pressure supply of fuel. The operation of fuel system  12  will now be explained. 
   Needle valve element  58  may be moved by an imbalance of force generated by fuel pressure. For example, when needle valve element  58  is in the first or orifice-blocking position, pressurized fuel from fuel supply passageway  74  may flow into control chamber  72  to act on hydraulic surface  98 . Simultaneously, pressurized fuel from fuel supply passageway  74  may flow into central bores  70  and  82  in anticipation of injection. The force of spring  88  combined with the hydraulic force generated at hydraulic surface  98  may be greater than an opposing force generated at hydraulic surface  100  thereby causing needle valve element  58  to remain in the first position to restrict fuel flow through orifices  84 . To open orifices  84  and inject the pressurized fuel from central bore  82  into combustion chamber  22 , first solenoid actuator  60  may move its associated valve element to selectively drain the pressurized fuel away from control chamber  72  and hydraulic surface  98 . This decrease in pressure acting on hydraulic surface  98  may allow the opposing force acting across hydraulic surface  100  to overcome the biasing force of spring  88 , thereby moving needle valve element  58  toward the orifice-opening position. 
   To close orifices  84  and end the injection of fuel into combustion chamber  22 , second solenoid actuator  62  may be energized. In particular, as the valve element associated with second solenoid actuator  62  is urged toward the flow blocking position, fluid from control chamber  72  may be prevented from draining to tank  28 . Because pressurized fluid is continuously supplied to control chamber  72  via restricted supply passageway  80 , pressure may rapidly build within control chamber  72  when drainage through control passageway  76  is prevented. The increasing pressure within control chamber  72 , combined with the biasing force of spring  88 , may overcome the opposing force acting on hydraulic surface  100  to force needle valve element  58  toward the closed position. It is contemplated that second solenoid actuator  62  may be omitted, if desired, and first solenoid actuator  60  used to initiate both the opening and closing motions of needle valve element  58 . 
   Actuator  104  may affect the pressure of the fluid supplied to central bores  70  and  82 , and injected into combustion chamber  22 . Specifically, in response to a current applied to the piezo electric crystals of actuator  104 , actuator  104  may affect movement of variable restrictive device  106  via communication link  110  to increase or decrease the restriction on the fluid flowing into fuel injector  32 . This change in the restriction may directly affect the pressure drop across variable restrictive device  106  and resulting pressure of fuel within central bores  70  and  82 . For example, an increased current applied to actuator  104  may cause a decrease in restriction of variable restrictive device  106  and a resulting higher pressure of fuel within central bores  70  and  82 . In contrast, a decreased current applied to actuator  104  may cause an increase in restriction of variable restrictive device  106  and a resulting lower pressure of fuel within central bores  70  and  82 . 
   The pressure of the fuel supplied to central bores  70  and  82 , and injected into combustion chamber  22  may be varied throughout a single injection cycle (e.g., the cycle of injections occurring during the four strokes of piston  18 ) or even during a single injection event. Specifically, as illustrated in  FIG. 3 , a first curve  114  may represent various injection events occurring within a single injection cycle, while a second curve  116  may represent the pressure of the fuel injected during each of the injection events. As can be seen from first and second curves  114 ,  116 , two pilot injections of fuel at a first pressure are illustrated as occurring before piston  18  has reached top dead center (TDC), three main injections of fuel at a second pressure are illustrated as occurring shortly after piston  18  has reached TDC, and two post injections of fuel at a third pressure are illustrated as occurring late in the downward stroke of piston  18 . As illustrated by a dashed line  118  associated with second curve  116 , the pressure within a single injection event may also be varied by changing the restriction of variable restrictive device  106  during the injection event. It is to be noted that the injection events depicted within  FIG. 3  are exemplary only and that any number of injections may implemented at any suitable timing relative to the motion of piston  18 . It also contemplated that the relative pressure magnitudes depicted by second curve  116  may be modified, as desired. 
   Because fuel system  12  may vary the pressure of injected fuel by changing the restriction placed on fuel supplied to fuel injectors  32 , the number of different levels of fuel pressure available for injection may be infinite. In particular, fuel system  12  is not limited to specific predetermined pressure levels. This flexibility in the pressure of injected fuel may extend the use of fuel system  12  to different applications, as well as extending the operational range and efficiency of engine  10 . In addition, this flexibility may allow compliance with emission standards under a wider range of operating conditions. 
   Further, because fuel system  12  may vary the pressure of injected fuel with a minimal number of additional components, the complexity and cost of fuel system  12  may be low. Specifically, the addition of actuator  104 , variable restrictive device  106 , and check valve  108  may add very little complexity or cost to fuel system  12 . 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the fuel system 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 fuel system 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.