Abstract:
A nozzle supply valve is positioned in the nozzle supply passage of a fuel injector, and is constructed to generate a boot shaped rate trace mechanically. The goal of the concept is to restrict the flow area during the first boot step and release the flow area restriction in the second step. During the first stage of injection, the flow to the nozzle only goes through a restricted orifice. When the line pressure is high enough to overcome the valve movement pressure spring preload, the nozzle supply valve moves to an unrestricted position, and the boot shaped rate trace is formed. Since this boot shape rate trace is generated mechanically, it can be combined with fuel injectors having a direct control needle valve in order to get different rate traces including, ramps, squares, pilots, posts and other split injections.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to front end rate shaping during fuel injection events, and more particularly to a valve concept for producing boot shaped injection rate trace profiles.  
         BACKGROUND  
         [0002]    Over the years, engineers have come to recognize that undesirable emissions can be lowered at different operating conditions by producing particular injection rate trace profiles. Among the various rate shape profiles are so called ramps, boots, squares and splits, etc. There are numerous references describing various fuel injection systems and the means by which they can produce one or more of the above identified rate shaping traces. For instance, commonly owned U.S. Pat. No. 5,462,030 to Shinogle shows a spring loaded device that can be employed in a fuel injection system in order to produce a front end rate shape that is somewhere between a boot and split injection rate trace. During an injection event, as fuel pressure is building after the nozzle outlet has opened, the Shinogle device includes a small spring loaded accumulater volume that opens at some pre-determined pressure. As fuel flows into the accumulater volume, the pressure, and hence the flow rate, at the nozzle outlet briefly drops. After the accumulator volume is full, the pressure and flow rate out of the nozzle outlet rise in a somewhat conventional manner. The end result is a particular front end rate shaping that is a function of several factors including the accumulator volume, its opening pressure, etc. The Shinogle device also appears to include some adjustment means for adjusting the rate shape produced by the device. While the Shinogle device appears to have a promise, there remains room for improvement.  
           [0003]    The present invention is directed to these and other problems associated with producing front end rate shaping in fuel injection systems.  
         SUMMARY OF THE INVENTION  
         [0004]    In one aspect, a fuel injector includes an injector body that defines a nozzle supply passage and a nozzle outlet. A needle valve member is positioned in the injector body and is moveable between an open position in which the nozzle supply passage is open to the nozzle outlet, and a closed position in which the nozzle supply passage is closed to the nozzle outlet. A nozzle supply valve member is positioned in the injector body and includes an opening hydraulic surface exposed to fluid pressure in an upstream portion of the nozzle supply passage. The nozzle supply valve member is moveable between a first position in which the nozzle supply passage is relatively restricted, and a second position in which the nozzle supply passage is relatively unrestricted.  
           [0005]    In another aspect, a fuel injection system includes a nozzle supply valve moveable between a first position in which a nozzle supply passage is relatively restricted, and a second position in which the nozzle supply passage is relatively unrestricted. The nozzle supply valve is biased by a first biaser toward its first position when fluid pressure in the nozzle supply passage upstream from the nozzle supply valve is below a first predetermined pressure. A nozzle outlet valve is moveable between an open position in which the nozzle supply passage is open to a nozzle outlet, and a closed position in which the nozzle supply passage is closed to the nozzle outlet. The nozzle outlet valve is biased by a second biaser toward its closed position when fluid pressure in the nozzle supply passage between the nozzle supply valve and the nozzle outlet valve is below a second predetermined pressure. The second predetermined pressure is lower than the first predetermined pressure.  
           [0006]    In still another aspect, a method of injecting fuel includes a step of opening a nozzle outlet at least in part by raising fuel pressure in a nozzle supply passage above a first predetermined pressure, and moving a needle valve member from a closed position toward an open position. Fuel flow in the nozzle supply passage is restricted. The flow restriction in the nozzle supply passage is then removed at least in part by increasing fuel pressure in the nozzle supply passage above a second predetermined pressure, which is greater than the first predetermined pressure, and by moving a nozzle supply valve member from a first position toward a second position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a schematic illustration of a fuel injection system according to one aspect of the present invention;  
         [0008]    [0008]FIG. 2 is a sectioned side diagrammatic view of a nozzle supply valve according to the preferred embodiment of the present invention;  
         [0009]    [0009]FIG. 3 is a graph of plunger pressure and sac pressure verses time for an example fuel injection event according to the present invention;  
         [0010]    [0010]FIG. 4 is a sectioned side diagrammatic view of a hydraulically actuated fuel injector according to another embodiment of the present invention; and  
         [0011]    [0011]FIG. 5 is a graph of plunger pressure and sac pressure verses time for an example fuel injection event according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0012]    Referring to FIG. 1, a fuel injection system  10  includes a fuel injector  12  and a fuel pressurizer  14 , which in this example is a unit pump  16 . A rotating cam  17  causes a plunger  18  to reciprocate in unit pump  16  to displace fluid into and out of a fuel pressurization chamber  25 . Unit pump  16  includes a conventional spill valve  20  which typically has two positions. In a first position, fuel is displaced from fuel pressurization chamber  25  at low pressure to a pump inlet/spill port  22 , for recirculation. When plunger  18  is undergoing its pumping stroke and spill valve  20  is closed, fuel in fuel pressurization chamber  25  is pressurized to injection levels and displaced toward fuel injector  12  via a pump outlet  21  and a nozzle supply passage  26 .  
         [0013]    Referring now in addition to FIG. 2, nozzle supply passage  26  can be thought of as including an upstream portion  27  separated from a downstream portion  28  by a nozzle supply valve  40 . Those skilled in the art will appreciate that nozzle supply valve  40  could be positioned at any suitable location in nozzle supply passage  26 , but is preferably located within injector body  12  in close proximity to a nozzle chamber  30 . When nozzle supply valve  40  is in its closed position as shown in FIG. 2, upstream portion  27  of nozzle supply passage  26  is connected to downstream portion  28  via a relatively restricted passage  42  defined by nozzle supply valve member  41 . Nozzle supply valve member  41  is biased toward this closed position in which its valve surface  44  is in contact with a conical valve seat  49  by a biaser, which is preferably a compressed spring  46 . When fuel pressure acting on an opening hydraulic surface  43  is above a first predetermined pressure, nozzle supply valve member  41  moves toward an open position against the action of spring biaser  46 . The maximum travel of nozzle supply valve member  41  is defined by a stop piece  45  which is preferably located in a spring chamber  47  along with biasing spring  46 . Spring chamber  47  is vented in order to prevent hydraulic locking via a vent  48 . Nozzle supply valve member  41  is guided in its movement by preferably having a matched clearance with a guide bore  51  defined by injector body  12 . Thus, when nozzle supply valve member  41  is in its closed position, as shown, nozzle supply passage  26  has a relatively restricted flow area due to restricted passage  42 . When nozzle supply valve member  41  moves to its open position, nozzle supply passage  26  has a relatively unrestricted flow area.  
         [0014]    Fuel injection system  10  also includes a nozzle outlet valve  32  that is positioned in injector body  12  between nozzle supply valve  40  and nozzle outlet  36 . Nozzle outlet valve  32  includes a needle valve member  34  that is biased to a downward closed position in a conventional manner by a biaser, which is preferably a compressed spring  37 . Those skilled in the art will appreciate that the identified biasers  37  and  46  could be any suitable force generating means, including but not limited to other mechanical device biasers, magnetic biasers and hydraulic biasers. When needle valve member  34  is in its downward closed position, sac  38  and nozzle outlet  36  are blocked from fluid communication with nozzle chamber  30 . Needle valve member  34  includes an opening hydraulic surface  35  exposed to fluid pressure in a nozzle chamber  30 . When fuel pressure in nozzle chamber  30  is above a second predetermined pressure, the fluid pressure on opening hydraulic surface  35  causes needle valve member  34  to lift to an open position that fluidly connects nozzle outlet  36  to nozzle chamber  30 . The first predetermined pressure at which nozzle supply valve  40  moves to its unrestricted position is preferably substantially higher than the second predetermined pressure at which nozzle outlet valve  32  moves toward its open position. For instance, the valve movement pressure (VMP) of the nozzle supply valve  40  could be on the order of about 100 MPa, while the valve opening pressure (VOP) of the nozzle outlet valve might be on the order of about 40 MPa. Thus, when in operation, nozzle outlet valve  32  will open first, and fuel will be supplied to nozzle outlet  36  via a relatively restricted flow area, and then flow will become unrestricted as pressure builds to a point that opens moves nozzle supply valve  40  to remove the flow restriction in nozzle supply passage  26 .  
         [0015]    Referring now to FIG. 4, an alternative embodiment of the present invention includes a hydraulically actuated fuel injector  60  that includes a substantially identical nozzle supply valve  40  positioned in its nozzle supply passage  84 . Fuel injector  60  includes a hydraulic fuel pressurizer  62 , a direct control nozzle outlet valve  64 , a flow control valve assembly  66  and a needle control valve  68  that are all positioned in and/or are attached to injector body  61  in a conventional manner. When in operation, flow control valve assembly  66  alternately exposes an intensifier piston  80  to a source of high pressure fluid and a drain in order to cause plunger  81  to reciprocate. Needle control valve  68  alternately exposes a closing hydraulic surface  92  of a needle valve member  90  to either high pressure or low pressure in order to open and close nozzle outlet  87 . Thus, flow control valve assembly  66  controls the pressurization of fuel in fuel injector  60 , while needle control valve  68  controls the timing, and to some extent rate shaping, of each injection event.  
         [0016]    Flow control valve assembly  66  includes an electrical actuator  67 , which like all of the electrical actuators identified with respect to the present invention could be a solenoid as illustrated, a piezo actuator or possibly some other suitable actuator such as a voice coil. Electrical actuator  67  is operably coupled to a pilot valve member  72  that is trapped between upper and lower seats to alternately connect a pressure control passage  77  to either high pressure or low pressure. Flow control valve assembly  66  also includes a spool valve member  73  with a biasing hydraulic surface  74  always exposed to high pressure, and a control hydraulic surface  75  exposed to fluid pressure in pressure control passage  77 . Pilot valve member  72  is normally biased to a downward position that fluidly connects pressure control passage  77  to high pressure via high pressure passage  71  to cause spool valve member  73  to be biased toward its upward position, as shown, by a biasing spring. When in this position, an actuation fluid passage  78  is connected to a low pressure drain  79  via an annulus feature on the outer surface of spool valve member  73 . When electrical actuator  67  is energized to pull pilot valve member  72  upward, pressure control passage  77  becomes fluidly connected to a low pressure vent, which allows the continuous high pressure on biasing hydraulic surface  74  to push spool valve member  73  downward to close drain  79  and open actuation fluid passage  78  to high pressure passage  71  via another annulus on the outer surface of spool valve member  73 .  
         [0017]    The upper hydraulic surface of intensifier piston  80  is exposed to fluid pressure in actuation fluid passage  78 . When actuation fluid passage  78  is connected to fluid drain  79 , a return spring  82  tends to bias and push intensifier piston  80  and plunger  81  upward toward their retracted positions, as shown. When actuation fluid passage  78  is connected to high pressure passage  71 , intensifier piston  80  and plunger  81  are driven downward to compress and pressurize fuel in a fuel pressurization chamber  83 . When plunger  81  is undergoing its upward return stroke, fresh low pressure fuel is drawn into fuel pressurization chamber  83  from fuel inlet  100  past a check valve that prevents reversed flow.  
         [0018]    Fuel pressurization chamber  83  is connected to one end of a nozzle supply passage  84  that includes at its other end a nozzle chamber  86 . Preferably, a nozzle supply valve  40  having a structure substantially identical to that previously described is positioned in nozzle supply passage  84  between fuel pressurization chamber  83  and nozzle chamber  86 . When needle valve member  90  is in its downward position as shown, sac  88  and nozzle outlet  87  are closed to nozzle chamber  86 . When needle valve member  90  lifts to its open position, nozzle outlet  87  and sac  88  are then open to nozzle chamber  86 .  
         [0019]    Needle valve member  90  includes an opening hydraulic surface exposed to fluid pressure in nozzle chamber  86 , and a closing hydraulic surface  92  exposed to fluid pressure in a needle control chamber  94 . Needle valve member  90  is normally biased to its downward position by an appropriate biaser, such as a compressed biasing spring  96  as shown. Needle control chamber  94  is fluidly connected to needle control valve  68  via a needle control passage  98 . Needle control valve  68  includes an electrical actuator  69 , and has a structure substantially similar to the pilot valve portion of flow control assembly  66 . When electrical actuator  69  is deenergized, needle control passage  98  is connected to high pressure passage  71 , which results in needle valve member  90  being held in its downward closed position even in the presence of high pressure fuel in nozzle chamber  86 . When needle control valve  68  is energized, needle control passage  98  becomes connected to a source of low pressure which will allow needle valve member  90  to lift toward its open position against the action of biasing spring  96  provided that fuel pressure in nozzle chamber  86  is above a valve opening pressure. Like the previous embodiment, the valve opening pressure of needle valve member  90  is preferably substantially lower than the valve movement pressure of nozzle supply valve  40 .  
       INDUSTRIAL APPLICABILITY  
       [0020]    Referring again to FIGS. 1 and 2, and in addition to FIG. 3, a pressure trace for an example fuel injection event according to the present invention is illustrated. Those skilled in the art will appreciate that an injection rate trace shape will have a shape very similar to the sac pressure rate trace illustrated in FIG. 3. This attribute allows a curve that is indicative of the injection flow rate to be mapped on top of the same graph that indicates fuel pressure in the upstream portion of the nozzle supply passage, which is identified in the graph as being at the plunger surface. Each injection event is initiated by the lobe of cam  17  turning to cause plunger  18  to begin displacing fuel from fuel pressurization chamber  25 . The pressurization portion of the injection event begins when spill valve  20  is closed. At that time, fuel pressure adjacent plunger  18  begins to rise. However, because fuel pressure has not yet reached the valve opening pressure of nozzle outlet valve  32 , the nozzle outlet valve remains closed and sac pressure remains low. As plunger  18  continues its pumping stroke, fuel pressure eventually exceeds the valve opening pressure (VOP) of nozzle outlet valve  32  causing it to open which results in the beginning of nozzle spray out of nozzle outlets  36  and a rise in sac pressure. This portion of the injection event is commonly referred to as the toe portion of a boot shaped injection event.  
         [0021]    As plunger  18  continues its pumping stroke, fuel pressure soon exceeds the valve movement pressure of the nozzle supply valve  40  causing it to move from its restricted position to its unrestricted position. This in turn results in the injection rate and the sac pressure ramping up accordingly for the instep portion of the boot rate shape. The injection event then continues at or near a maximum fuel pressure. Shortly before the desired end to the injection event, spill valve  20  is again opened to spill fuel pressure in fuel pressurization chamber  25  and nozzle supply passage  26 . This drop in fuel pressure causes needle valve member  30  and outlet valve  32  to close under the action of biasing spring  37  to end the injection event.  
         [0022]    Referring now to FIGS. 4 and 5, between injection events, electrical actuator  67  and  69  are deenergized; this results in actuation fluid passage  78  being connected to low pressure drain  79 , and needle control passage  98  being connected to high pressure passage  71 . Those skilled in the art will recognize that fuel injector  60  is capable of doing several different types of injection rate traces, including boot shaped injections, ramps, squares, splits, etc. In order to produce a boot shaped injection of the type shown in FIG. 5, both electrical actuators  67  and  69  are energized close in time. This connects needle control passage  98  to low pressure so that the only force holding needle valve member  90  in its downward closed position is biasing spring  96 . When electrical actuator  67  is energized, pressure control passage  77  becomes connected to low pressure which cause spool valve member  73  to be pushed downward to closed low pressure drain  79 , and open actuation fluid passage  78  to high pressure passage  71 . When this occurs, high pressure flows into actuation fluid passage  78  and pushes intensifier piston  80  and plunger  81  downward to compress fuel in fuel pressurization chamber  83 .  
         [0023]    As plunger  81  begins its downward stroke, fuel pressure in nozzle supply passage  84  and fuel pressurization chamber  83  builds. When that pressure exceeds the valve opening pressure of nozzle outlet valve  64 , needle valve member  90  lifts to its open position to commence the spraying of fuel, beginning the toe portion of a boot shaped rate event. As plunger  81  continues its pumping stroke, fuel pressure continues to rise and eventually exceeds the valve movement pressure of nozzle supply valve  40 , causing it to move from its restricted position to an unrestricted position. This begins the instep portion of the boot, and the injection event continues in a conventional manner. Shortly before the desired amount of fuel has been injected, electrical actuator  69  is deenergized to reconnect needle control passage  98  to high pressure in order to quickly push needle valve member  90  downward toward its closed position due to the high pressure now acting on closing hydraulic surface  92 .  
         [0024]    Thus in both embodiments of the present invention, the nozzle outlet is opened by raising fuel pressure in a nozzle supply passage above a first predetermined pressure and by moving the needle valve member from a closed position to an open position. When fuel commences to spray, it is supplied to the nozzle outlet via the nozzle supply passage which has a flow restriction. During the injection event, the flow restriction is removed by increasing fuel pressure in the nozzle supply passage above a second predetermined pressure which causes the nozzle supply valve member to move from a first or restricted position to a second or unrestricted position. In both of the illustrated embodiments, the step of raising fuel pressure and the step of increasing fuel pressure are accomplished by driving a plunger away from a retracted position toward an advanced position. However, those skilled in the art will appreciate that the present invention could be used in conjunction with a common rail system in which some intervening device (e.g. valve) between the common rail and the fuel injector causes fuel pressure in the nozzle supply passage to build gradually in a way that mimics the pressure build up produced by a reciprocating plunger.  
         [0025]    In both embodiments of the present invention, a nozzle supply valve having a similar structure is illustrated in which the restricted passage is defined by the nozzle supply valve member itself. Those skilled in the art will appreciate that the restricted passage according to the present invention need not necessarily be defined by the nozzle supply valve member, but instead could be defined by the injector body, or by both the valve member and the injector body. Preferably, the unrestricted flow through the nozzle supply passage is produced by moving the nozzle supply valve member away from a conical valve seat to open relatively unrestricted flow across the valve seat. In the illustrated embodiments, the various biasers are shown as compressed springs; however, those skilled in the art will appreciate that other biasers, such as other mechanical devices, magnetic devices or possibly even hydraulic fluid pressure could be used to bias the various members toward one position. The present invention is aimed at creating an ability to generate boot shaped rate traces mechanically. The idea of this concept is to restrict the flow area during the first boot step and then release or unrestrict the flow area in the second boot step. The concept is simple in design and in manufacture.  
         [0026]    It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. Thus, those skilled in the art will appreciate that other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.