Abstract:
A common rail single fluid injection system includes fuel injectors and control valve assemblies with an internal cooling fluid circuit to improve overall life and performance of the injector. This is accomplished by supplying cooling fluid to the injector and allowing the same to come in direct contact with one of the hottest locations within the fuel injector; the high-pressure leak split spot. By providing cooling fluid directly to this location and then allowing the cooling fluid to drain out of the injector, the present disclosure effectively and efficiently manages thermal loads within the injector.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to a single fluid fuel injection system, and more particularly to a fuel injector and a control valve assembly capable of controlling thermal loads. 
       BACKGROUND 
       [0002]    Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, exhaust a complex mixture of combustion related constituents. The constituents may be gaseous and solid material, which include nitrous oxides (NOx) and particulate matter. Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of NOx and particulate matter emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. 
         [0003]    Engineers have come to recognize that common rail fuel systems may be used to improve diesel engine emissions and performance. Common rail fuel systems can provide high injection pressure, flexible injection modes, such as multiple injections, and may be operated independently of engine speed. However, because of the high pressures associated with common rail fuel systems, the same may have an increased risk of fuel leakage. Leakage of fuel at high pressures tends to generate heat, which is then transferred to the injector components. This heat may increase the temperature and may change the material properties of the injector components. In certain instances, the temperature may become high enough to cause fuel to decompose and become unstable or oxidated within the high-pressure fuel system. This may lead to fuel deposits being formed on injector components, such as control valves. These deposits may inhibit the movement of control valve components by causing the same to become sticky or stuck. This may lead to control valve failure and ultimately injector failure. 
         [0004]    To meet increasingly stringent emissions regulations, engine manufacturers have utilized multiple injections of fuel into the combustion chamber during any particular combustion event. The multiple injections may include a pilot injection, a main injection, and/or a post injection. In most cases, multiple injections may be achieved by controlling the actuation of a control valve multiple times during any given combustion cycle. In order to achieve these multiple actuation events, additional electrical energy is required. The increased number of valve actuations may lead to more leakage of high-pressure fuel within the fuel injector. Increased leakage may further increase the internal temperature of an injector. 
         [0005]    The use of multiple injection events and higher fuel pressures may have a significant impact on the magnitude of the heat energy to which components of fuel injections. One of the hottest locations within a fuel injector is the high-pressure leak split spot. This spot is located at or near the center of a control valve. Rising temperatures within a control valve may lead to failure of solenoids if the fuel injector is not cooled sufficiently. It would be desirable to cool a fuel injector in such a manner that the temperature of the high-pressure leak split spot is controlled. 
         [0006]    An example of a previous attempt to cool a fuel injector is disclosed in U.S. Pat. No. 6,360,963 to Popp. In that disclosure, openings in the form of the cross holes are drilled into the sleeve of the needle chamber. These cross-holes are provided to allow gaseous fuel to cool the exposed surface of the needle valve. While this disclosure may work to keep the injector needle and tip cooler, it does nothing to address the temperature within the hottest location of the injector; the high-pressure leak split spot. Thus, the control valve may still be susceptible to failure due to excessive temperatures. 
         [0007]    The disclosed fuel injector and control valve assembly with thermal load control is directed to overcoming one or more of the problems set forth above. 
       SUMMARY OF THE DISCLOSURE 
       [0008]    In one aspect, a fluid injector including an injector body defining a cooling fluid supply inlet, a high-pressure fluid supply inlet, and a drain. The injector also includes a control valve assembly at least partially disposed within the injector body, and fluidly coupled to the high-pressure fluid supply inlet, the cooling fluid supply inlet, and the drain. The control valve further includes a valve body having an opening for receiving a valve stem. An electrical actuator at least partially disposed within the valve body is also included in the control valve. The control valve further includes an armature coupled to a valve stem, wherein the valve stem is at least partially disposed within the valve body. A load screw disposed above the valve body and having an opening for receiving a valve stem is also included. The control valve also includes a radial passage fluidly coupling a high-pressure leak split spot, the cooling fluid supply inlet, and the drain. 
         [0009]    In another aspect, a method of cooling a fluid injector including the steps of providing an injector body defining a cooling fluid supply inlet, a high-pressure fluid supply inlet, and a drain. Also provided is a control valve assembly at least partially disposed within the injector body, fluidly coupled to the high pressure fluid supply inlet, the cooling fluid supply inlet, and the drain. The control valve further includes a valve body having an opening for receiving a valve stem. Also included is a valve stem at least partially disposed within the valve body. The control valve further includes a load screw having an opening for receiving a valve stem. The method also includes a step of supplying cooling fluid to a high-pressure leak split spot. A step of draining cooling fluid away from the high-pressure leak split spot and out of the injector is also a part of the method. 
         [0010]    In another aspect, an internal combustion engine including an engine housing defining a plurality of engine cylinders, and including a plurality of pistons each being movable within a corresponding one of the engine cylinders. Also included is a fuel system having a plurality of fuel injectors associated one with each of the plurality of engine cylinders, each of the fuel injectors including an injector body and a control valve, wherein each injector body defines a cooling fluid supply inlet, a high pressure fuel supply inlet, and a drain. Each control valve assembly is at least partially disposed within the injector body, and is fluidly coupled to the high pressure fuel supply inlet, the cooling fluid supply inlet, and the drain, and further includes a valve body having an opening for receiving a valve stem. The control valve also includes an electrical actuator and an armature coupled to a valve stem, wherein the valve stem is at least partially disposed within the valve body. The control valve also includes a load screw disposed above the valve body and having an opening for receiving a valve stem. The control valve also includes a radial passage fluidly coupling a high-pressure leak split spot, the cooling fluid supply inlet, and the drain. 
         [0011]    In another aspect, a control valve assembly including a cooling fluid supply, and a valve body having an opening for receiving a valve stem. The control valve assembly further includes an electrical actuator and an armature coupled to a valve stem, wherein the valve stem is at least partially disposed within the valve body. A load screw disposed above the valve body and having an opening for receiving a valve stem is also included. The control valve further includes a radial passage fluidly coupled to the cooling fluid supply and a high-pressure leak split spot. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a diagrammatic schematic of a fuel system using a common rail fuel injector according the present disclosure; 
           [0013]      FIG. 2  is a cross section of a common rail fuel injector utilizing an exemplary control valve assembly with thermal load control according to present disclosure; 
           [0014]      FIG. 3  is a detail view of an exemplary control valve assembly according to the present disclosure; 
           [0015]      FIG. 4  is a plan view of the upper surface of an exemplary load screw according to the present disclosure; 
           [0016]      FIG. 5  is a plan view of the lower surface of an exemplary load screw according to the present disclosure; 
           [0017]      FIG. 6  is a side view of an exemplary load screw according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring to  FIG. 1 , a fuel system utilizing a common rail fuel injector  10  is shown. A reservoir  12  contains fuel at an ambient pressure. A transfer pump  14  draws low-pressure fuel through fuel supply line  16  and provides it to a cooling fuel supply line  18 . Cooling fuel supply line  18  provides low-pressure fuel to injectors  10  for cooling purposes. Those skilled in the art will recognize that cooling fuel can be supplied to the injectors either in parallel or in series without departing from the nature and scope of this disclosure. If cooling fuel is supplied in parallel, each injector receives cooling fluid directly from the reservoir  12 . Alternatively, if cooling fuel is supplied in series, only the first injector receives cooling fuel from the reservoir. When that cooling fuel is drained, it is then supplied to the next injector in the series and so on down the line. 
         [0019]    Within each injector  10 , low-pressure fuel is routed through a cooling circuit (described in greater detail below) wherein low-pressure fuel is routed past a high-pressure leak split spot  20  (See  FIGS. 2 and 3 ) and drained out of the injector  10 . Drained fuel is ultimately returned to the reservoir  12  via a fuel return line  22 . 
         [0020]    Transfer pump  14  also provides low-pressure fuel to high-pressure pump  24 . High-pressure pump  24  then pressurizes the fuel to desired fuel injection pressure levels and delivers the fuel to the fuel rail  26 . The pressure in fuel rail  26  is controlled in part by safety valve  28 , which spills fuel to the fuel return line  22  if the pressure in the fuel rail  26  is above a desired pressure. The fuel return line  22  returns fuel to reservoir  12 . 
         [0021]    Fuel injector  10  draws fuel from fuel rail  26  and injects it into a combustion cylinder of the engine (not shown). Fuel not injected by injector  10  is spilled to fuel return line  22 . Electronic Control Module (ECM)  30  provides general control for the system. ECM  30  receives various input signals, such as from pressure sensor  32  and a temperature sensor  34  connected to fuel rail  26 , to determine operational conditions. ECM  30  then sends out various control signals to various components including the transfer pump  14 , high-pressure pump  24 , and fuel injector  10 . 
         [0022]    Referring to  FIG. 2 , the internal structure and fluid circuitry of each fuel injector  10  is illustrated. In particular, an injector body  36  defines a high-pressure fuel supply inlet  38  and a nozzle fuel supply passage  40  and a control valve supply passage  42  which are interconnected. Nozzle fuel supply passage  40  is in fluid communication with nozzle chamber  44 . Control valve supply passage  42  is in fluid communication control valve assembly  46 . Disposed within nozzle chamber  44  is a check needle  48 . The check needle  48  has a first end  50  and a second end  52 . The check needle  48  is movable between a first and second position. In a first position, the first end  50  of the check needle  48  rests on seat  54 , which in a first position, rests on seat  54  and blocks at least one orifice  56  located in the injector tip  58 . Biasing spring  49  biases check needle  48  toward its first position. As will be explained in greater detail below, in its second position, the first end  50  of the check needle  48  at least partially unblocks the at least one orifice  56 , thereby allowing fuel to be injected into a combustion chamber (not shown). 
         [0023]    Injector body  36  also defines a check control passage  60 . Check control passage  60  is in fluid communication with check control chamber  62 . The second end  52  of check needle  49  is disposed within the check control chamber  62 . The check control passage  60  is also in selective fluid communication with control valve supply passage  42 , via control valve assembly  46 . Control valve assembly  46  may also selectively put check control passage  60  in fluid communication with a drain passage  64  and drain outlets  66 . 
         [0024]    The operation of the fuel injector  10  is controlled at least in part by control valve assembly  46 . As seen in  FIGS. 2 and 3 , at least a portion of control valve assembly  46  may be disposed within the injector body  36  of injector  10 . Control valve assembly  46  may include an upper valve body  68 , a lift plate  70 , and a lower valve body  72 . The upper valve body  68 , lift plate  70 , and lower valve body  72  may be held together by a securing mechanism or screw  74 . The control valve assembly  46  may further comprise a load screw  76 . The load screw  76  is disposed atop the upper valve body  68  and may have threaded sides  77  to allow it to be screwed into mating threads (not shown) on the injector body. When in position, the load screw  76  applies a downward force on the upper valve body  68 , lift plate  70 , and lower valve body  72 , thereby minimizing their movement within injector body  36 . 
         [0025]    Control valve assembly  46  may further include an armature  78  coupled to a valve stem  80 . Armature  78  may be disposed atop the load screw  76 . Valve stem  80  may be disposed within an opening that extends through the load screw  76 , upper valve body  68 , lift plate  70 , and lower valve body  72 . Valve stem  80  may be movable between a low-pressure seat  82  and a high-pressure seat  84 . A biasing spring  85  biases valve stem  80  toward the low-pressure seat  82 . When valve stem  80  is on the low-pressure seat  82 , check control passage  60  is in fluid communication with control valve supply passage  42 . Conversely, when valve stem  80  is on the high-pressure seat  84 , check control passage  60  is in fluid communication with drain passage  64 . 
         [0026]    Control valve assembly  46  may further include an electrical actuator  86 . The electrical actuator  86  depicted in  FIGS. 2 and 3  is a solenoid. However, those skilled in the art will recognize that other types of electrical actuators, such as piezoelectric devices may be used without departing from the scope of this disclosure. 
         [0027]    The operation of injector  10  will now be explained. The opening and closing of check needle  48  is controlled in part the presence of high pressure fuel in nozzle fuel supply passage  40 , and the check control passage  60 . Biasing spring  49  also plays a role in opening and closing of check needle  48 . When an injection event is not desired, the electrical actuator  86  of control valve assembly  46  is not energized. High-pressure fuel enters injector  10  through high-pressure fuel inlet  26 . Pressurized fuel is provided to control valve assembly  46 , via control valve supply passage  42 . In its deenergized state, control valve assembly  46  provides fluid communication between control valve supply passage  42  and check control passage  60 . Thus, high-pressure fuel from check control passage  60  provides a hydraulic load on the second end  52  of check needle  48 . The hydraulic load will keep check needle  48  closed such that the first end  50  of check needle  48  maintains contact with seat  54  and no fuel is injected out of orifice  56 . 
         [0028]    When injection is desired, the electrical actuator  86  of control valve assembly  46  is energized. The electrical actuator depicted in  FIGS. 2 and 3  is a solenoid. Thus, when energized, electrical actuator  86  creates an electromagnetic field, which causes armature  78  to overcome the force of biasing spring  85  and lift. Valve stem  80 , which is coupled to armature  78 , is then moved to its upper position or high-pressure seat  84 . In this position, pressurized fuel from control valve supply passage  42  is no longer in fluid communication with check control passage  60 . Instead, check control passage  60  is in fluid communication with drain passage  64 . High-pressure fuel is thus drained out of the check control passage  60  and the hydraulic load that was applied to the second end  52  of check needle  48  begins to decay. As the hydraulic load is decayed high pressure fuel from nozzle fuel supply passage  40  will apply hydraulic forces to the surfaces of the check needle  48  causing the same to open and begin to inject fuel into an engine cylinder (not shown). 
         [0029]    When it is desirable to stop injection, electrical actuator  86  is deenergized. As the electromagnetic field generated by electrical actuator  86  dissipates, the force of biasing spring  85  acts on armature  78 , and valve stem  80  is returned to close the low-pressure seat  82 . When the valve stem  80  is on the low-pressure seat  82 , the check control passage  60  is again in fluid communication with the control valve supply passage  42 . Ultimately, a hydraulic load is once again applied on second end  52  of check needle  48 . Thus, the first end  50  of check needle  48  is forced back into contact with seat  54  and orifice  56  is blocked. 
         [0030]    During an injection event, when valve stem  80  is on the high-pressure seat  84 , high-pressure fuel may tend to leak. Exemplary pressures of fuel that may leak may be up to and in excess of 190 MPa. At these high pressures, the fuel that leaks tends to migrate toward areas in the injector where the pressure is lower. One such location is known as the high-pressure leak split spot  20 . This location may be defined generically as any location along the valve stem that leaking pressurized fuel migrates to. Specifically, as depicted in  FIGS. 2 and 3 , the high-pressure leak split spot may be defined as the interface between the upper valve body  68 , load screw  76 , and the valve stem  80 . Thus, pressurized that leaks from the high-pressure seat  84 , may migrate through the upper valve body  68  to the high-pressure leak split spot. 
         [0000]    Leakage of fuel that occurs at these elevated pressures tends to generate excessive heat. This heat may be transferred to other injector components including the valve stem  80  and the electrical actuator  86 . Excessive heat transferred to injector components increases their temperature, and may change component material properties. Thus, injector performance and life may be adversely affected. 
         [0031]    Although not quite as common, leakage of high-pressure fuel may also occur when valve stem  80  is on the low-pressure seat  82 . Thus, high-pressure fuel may leak when fuel from the control valve supply passage  42  is in fluid communication with check control passage  60 . This high-pressure fuel may also migrate up the valve stem  80  through the upper valve body  68  to the high-pressure leak split spot  20 . This leakage may also generate excessive heat and have adverse affects on injector components and performance. 
         [0032]    A cooling system within individual fuel injectors  10  may be useful in combating excessive temperatures and controlling injector component temperatures. Injector body  36  may further define a cooling fluid inlet  88  coupled to a cooling fluid supply passage  90 . Cooling fluid supply passage  90  routes relatively cool low-pressure fuel to the control valve assembly  46  to keep the temperature of injector  10  down. Specifically, cooling fluid supply passage  90  provides relatively cool low-pressure fuel to a load screw reservoir  92 . The load screw reservoir  92  may be a bowl shaped receptacle defined by the load screw  76 . The load screw reservoir  92  has an opening  81  in which valve stem  80  is disposed. 
         [0033]    The cooling fuel that is supplied to the load screw reservoir  92  seeps down the sides  83  of valve stem  80  to the high-pressure leak split spot  20 . The high-pressure leak split spot may often be the hottest location within the fuel injector  10 . By routing low pressure cooling fuel directly to this location, thermal load control within the injection  10  is effectively and efficiently managed. Excessive heat from the high-pressure leak split spot  20  is transferred to the low pressure cooling fuel that is supplied thereto. This low pressure cooling fuel then travels through a radial passage  94  to an annular clearance  96 , which may be defined as the space between the injector body  36  outer edges of the upper valve body  68 , lift plate  70  and lower valve body  72 . The radial passage  94  and annular clearance  96  are in fluid communication with drain passage  64 . Thus, the low pressure cooling fuel is ultimately drained out of injector  10  through drain passage  64  and drain outlets  66 . 
         [0034]    Radial passage  94  carries low pressure cooling fuel away from the high-pressure leak split spot  20 . It is thus sized to effectively carry away at least as much mass flow of cooling fuel as is provided thereto. Additionally, radial passage  94  may be formed in a variety of manners so long as it provides fluid communication between the low-pressure fuel inlet  90 , the high-pressure leak split spot  20 , drain passage  64 , and drain outlets  66 . 
         [0035]    For example, as depicted in  FIGS. 2 ,  3 ,  5  and  6 , the lower surface  98  of load screw  76  may have one or more protrusions  100 . These protrusions  100  prevent the lower surface  98  of the load screw  76  from resting flush against an upper surface  102  of the upper valve body  68 . Instead, the protrusions  100  of load screw  76  are in contact with upper surface  102 . In this manner, radial passage  94  is created by the space between the lower surface  98  of load screw  76  and the upper surface  102  of upper valve body  68 . Although not shown, those skilled in the art will recognize that radial passage  94  may alternatively be formed if protrusions are disposed on the upper surface  102  of upper valve body  68 . Likewise the radial passage  94  may also be formed if protrusions are disposed on both the lower surface  98  of the load screw  76  and the upper surface  102  of the upper valve body  68 . 
         [0036]    Radial passage  94  may alternatively be formed without protrusions. For example, one or more channels or radial indentations could be cut into surfaces  98  and/or  102 . These channels or radial indentations would run along either or both surfaces  98  and  102  from the high-pressure leak split spot  20  to the annular clearance  96 . Further, the channels or radial indentations would be sized such that they could effectively handle the flow of low pressure cooling fuel provided thereto by the cooling fluid supply passage  90 . In yet another embodiment, radial passage  94  may be formed by drilled holes that run from the high-pressure leak split spot  20  through either the load screw  76 , or one or more of the upper valve body  68 , lift plate  70 , and lower valve body  72 . 
       INDUSTRIAL APPLICABILITY 
       [0037]    The present disclosure finds a preferred application in common rail fuel injection systems. In addition, the present disclosure finds preferred application in single fluid, namely fuel injection systems. Although the disclosure is illustrated in the context of a compression ignition engine, the disclosure could find application in other engine applications, including but not limited to spark ignited engines. The disclosed fuel injectors reduce the operating temperature of fuel injectors by utilizing a cooling system that directs cooling fuel to the high-pressure leak split spot, one of the hottest locations within an injector. In so doing, consistent reliable operation of injector components is achieved. 
         [0038]    In a preferred embodiment, fuel injector  10  receives low-pressure fuel cooling fuel via the cooling fuel supply line  18  and transfer pump  14 . This cooling fuel comes into injector  10  at the cooling fluid inlet  88 . The cooling fluid inlet  88  is fluidly coupled to a cooling fluid supply passage  90 . Cooling fluid supply passage  90  runs from the cooling fluid inlet  88  through the injector body  36  to the control valve assembly  46 . Specifically, the cooling fluid supply passage  90  provides cooling fuel to load screw reservoir  92 . Valve stem  80  is also disposed within the load screw reservoir  92 . Cooling fuel is allowed to run down the sides  83  of valve stem  80  until it reaches the high-pressure leak split spot  20 . The high-pressure leak split spot is one of the hottest locations within the injector  10 . Cooling fuel provided to the high-pressure leak split spot then travels along a radial passage  94  to an annular clearance  96 . From there, cooling fuel is routed to drain passage  64  and out of the injector  10  via drain outlets  66 . From there, the cooling fluid is ultimately returned to the reservoir  12 . 
         [0039]    The injector of the present disclosure controls thermal load within a common rail fuel injector by utilizing the aforementioned internal cooling circuit. In so doing, the control valve assembly  46  is cooled as is the high-pressure leak split spot  20 , which is one of the hottest locations within the injector. By providing cooling fuel directly to the high-pressure leak split spot, the injector of the present disclosure provides for an effective transfer of thermal energy. For example, laboratory tests have shown that injectors that do not utilize the cooling method as described in this disclosure may operate at temperatures between 150-160° C., while injectors that utilize the disclosed method may operate at 100-110° C. By operating at a significantly lower temperature, a more consistent and reliable injector performance can be achieved. 
         [0040]    The above description is intended for illustrative purposes only and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate the various modifications that can be made to the illustrated embodiments without departing from the spirit and scope of the disclosure, which is defined in the terms of the claims set forth below.