Abstract:
Controlling fuel injectors to create varying injection rates and injection rate shapes typically involves using multiple control valves to control fuel pressure and check valve opening pressure independently. The fuel injector of this application uses a single control valve positioned between a fuel supply passage and a tip supply passage. The control valve has at least three positions. In a second position allowing a first maximum fuel injection rate and allowing a second maximum fuel injection rate in a third position.

Description:
TECHNICAL FIELD  
         [0001]    This relates to an internal combustion engine and more specifically to a method and apparatus for controlling a fuel injector.  
         BACKGROUND  
         [0002]    Improved fuel injection systems allow internal combustion engines to increase fuel economy, reduce noxious emissions such as NOx and particulate matter, and increase power. Some of these gains come through increasing pressures of the fuel prior to injection into a combustion chamber. Increased pressures allow for more complete atomization of the fuel to increase the surface area of the fuel. The increased surface area promotes fuller combustion. Increasing the pressure of the fuel at the combustion chamber is accomplished in a number of manners including hydraulic intensification as shown in U.S. Pat. No. 6,305,358 issued to Lukich on Oct. 23, 2001. An alternative system uses an improved fuel pump to deliver high pressure fuel to a common fuel rail as shown in U.S. Pat. No. 5,497,750 issued to Mueller et al on Mar. 12, 1996. In both systems, timing of a fuel injection event may determined by electronic control of a valve such as movement of a solenoid.  
           [0003]    However, providing a directly operated check valve or DOC valve provides an additional benefit of more controllability of the fuel injection system.  
           [0004]    With a DOC valve, the fuel pressure as well as timing may be varied to create a fuel injection rate shape. By controlling the delivery of hydraulic fluid to a cavity over a check valve, a valve opening pressure needed to open the check valve may be varied. This increased controllability allows the fuel injection system to further lower engine noise and reduce emissions. Fuel from the common rail may also be used in a similar manner.  
           [0005]    Control of DOC valve generally requires precise machining including numerous passages machined or cast into an injector body. Improved controllability typically involves using multiple control valves. The additional machining and control valves increase costs of the fuel injection system. Further, multiple control valves may increase actual size of a fuel injector reducing space on a cylinder head of an engine for other needed hardware.  
           [0006]    The present invention is directed to overcoming one or more of the problems as set forth above.  
         SUMMARY OF THE INVENTION  
         [0007]    In one embodiment of the present invention, a fuel injector includes an injector body defining a fuel supply passage, and a tip supply passage. A fuel reservoir is positioned between the fuel supply passage and the tip supply passage. A check valve is positioned in a nozzle portion of the injector body ( 62 ). The check valve has a head portion and a tip portion. A nozzle reservoir is defined by the nozzle portion and the tip portion and head portion of the check valve. The tip supply passage is in fluid communication with the nozzle reservoir. A control valve is positioned in the fuel reservoir and is control movable to at least a first position, a second position, and a third position. The first position substantially inhibits fluid communication between the fuel supply passage and tip supply passage. The second position restricts fluid communication between the fuel supply passage and the tip supply passage. Fluid communication is allowed between the fuel supply passage and the tip supply passage in the third position.  
           [0008]    In another embodiment of the present invention, a fuel system includes a fuel pump in fluid communication with a fuel supply passage. A tip supply passage is in fluid communication with the fuel supply passage. A nozzle reservoir is in fluid communication with the tip supply passage. The nozzle reservoir is defined by a nozzle portion and a check valve. A control valve is disposed between the fuel supply passage and said tip supply passage. The control valve is movable to at least a first position, a second position, and a third position. In the first position fluid communication is substantially inhibited between the fuel supply passage and the tip supply passage. The second position restricts fluid communication between the fuel supply passage and the tip supply passage. The third position allows fluid communication between the fuel supply passage and the tip supply passage.  
           [0009]    In yet another embodiment, a method for controlling a fuel injector includes determining an engine operating condition. A control input is sent to the fuel injector. A control valve is positioned according to the control input in one of at least three positions. In the second position a first maximum fuel rate is allowed. The third position allows a second maximum fuel rate. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a schematic drawing of a fuel system embodying the present invention;  
         [0011]    [0011]FIG. 2 is a schematic drawing of a fuel injector embodying the present invention;  
         [0012]    [0012]FIG. 3 is a cross section of a control valve from the fuel injector of FIG. 2; and  
         [0013]    [0013]FIG. 4 is a graph of aspects with respect to time of the fuel injector embodying the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]    A fuel injection system  10  as shown in FIG. 1 includes a fuel tank  12 , a fuel pump  14 , fuel manifold or fuel rail  16 , a controller  18 , and at least one fuel injector  20 . A tank supply conduit  22  connects the fuel tank  12  with the fuel pump  14  in a conventional manner. The fuel pump  14  may be replaced by individual pumps for each fuel injector  20  such as cam actuated mechanical unit injectors. Optionally, a fuel lift pump  24  may also connect to the tank supply conduit  22  upstream of the fuel pump  14 . A fuel conduit  26  connects the fuel pump  24  with a fuel manifold  16 . While this application shows a single fuel manifold  16 , each injector  20  may connect with its own fuel manifold  16  or the fuel manifold  16  may connect with some subset of the fuel injectors  20 .  
         [0015]    In this application, the controller  18  is a conventional electronic control unit. The controller  18  receives a fuel signal  46  from a fuel sensor  48  that may be placed anywhere in the fuel system such as the fuel manifold  16 , fuel conduit  26 , or the fuel injector  20 . The fuel sensor may be adapted to measure one or more conditions of the fuel such as fuel pressure, fuel temperature, or fuel viscosity. The controller  18  also receives one or more engine condition signals  50  from engine sensors (not shown). The engine condition signals are indicative of typical conditions such as air manifold pressure, engine speed, engine load, fuel demand, air humidity, exhaust gas temperature, and air temperature.  
         [0016]    The fuel injector  20  as shown in FIGS. 2 and 3 includes a fuel supply passage  28 , a control valve  30 , a tip supply passage  32 , a nozzle portion  34 , and a check valve  36 . The fuel supply passage  28  fluidly connects with the fuel manifold  16 . The control valve  30  has at least three positions. In both the second and third position the tip supply passage  32  and fuel supply passage  28  are in fluid communication. However, in the first position the tip supply passage  32  and fuel supply passage  28  are substantially inhibited from fluid communication. In the second position the fluid communication between the fuel supply passage  28  and the tip supply passage  32  is restrictive when compared to the third position. An additional flow restriction  37  such as a venturi nozzle or orifice plate may also be place in the tip supply passage  32  between the control valve  30  and the nozzle portion  34 .  
         [0017]    The check valve  36  is positioned in the nozzle portion  34 . The check valve  36  has a head portion  38  and a tip portion  40  distal from the head portion  38 . The tip portion  40  is proximate to a seating portion  42  of the nozzle portion  34 . The nozzle portion  34  and check valve  36  define a nozzle reservoir  44  between said head portion  38  and said tip portion  40 . In an embodiment, a spring  45  is connected to the head portion  38 .  
         [0018]    As shown in FIG. 3, the control valve  30  in an embodiment is positioned in an injector body  62 . The control valve  30  includes a valve actuator  64  and a poppet  66  having an actuation portion  68  and a control portion  72 . The control portion  72  includes a first control seal portion  74  and a second control seal portion  76 . The injector body  62  includes a first body seal portion  78  and a second body seal portion  80 . The poppet  66  is movable in said injector body  62  between the first position of the control valve (where the first control seal portion  74  is in sealing connection with the first body seal portion  78 ) and the third position (where the second control seal portion  76  is in sealing connection with the second body seal portion  80 ). The poppet  66  and injector body  62  define a fuel reservoir  82  that may fluidly connect the fuel supply passage  28  with the tip supply passage  32 . While this embodiment shows a sliding poppet  66 , any conventional valve operation may be used such as a rotating valve or spool valve.  
         [0019]    The actuation portion  64  for this embodiment includes a solenoid  84  and an armature  86 . The solenoid  84  operates at multiple power levels such as multiple currents or voltages. The armature  86  connects with the actuation portion  68  in a conventional manner. The controller  18  provides a control input  88  to the solenoid  84 . Alternatively, the actuation portion  68  may be any conventional actuation mechanism such as a piezo-electric actuator.  
         [0020]    In an embodiment, the control input  88  to the solenoid  84  as shown in FIG. 4A (shown with respect to time) is one of four currents “a”, “b”, “c”, or “d”. Currents “a”, “c”, and “d” correspond with armature positions “a”, “b”, “c” respectively as shown in FIG. 4B. The first position of the control valve  30  corresponds with armature position “a”. The third position of the control valve  30  corresponds with armature position “c”. FIG. 4C shows a boot shape fuel injection rate curve where the check valve  36  is connected only with the spring  45 . The boot type fuel injection rate curve “F” is shown having a stable injection rate having a first maximum flow rate “a” followed by a ramp injection rate having a second maximum flow rate “b”. The fuel injector  20  may be instead used to create only the stable injection rate “a” or the ramp injection rate “b” or other combinations of conventional fuel injection shapes such as a post injection or pilot injection (not shown) at either the first maximum flow rate or the second maximum flow rate.  
       INDUSTRIAL APPLICABILITY  
       [0021]    In operation fuel flows from the fuel tank  12  into the fuel pump  14  where fuel pressure is increased to pressures suitable for atomizing liquid fuel as it exits the nozzle portion  34  of the fuel injector  20 . The fuel lift pump  24  may be used to transmit fuel to the fuel pump  14 . Fuel passes through the fuel conduit  26  into the fuel manifold  16  where high pressure fuel may be stored or accumulated prior to entering the fuel injector  20 . Alternatively, fuel may be pressurized after exiting the fuel manifold  16  in cases where the fuel pump  14  is associated with a fuel injector  20 .  
         [0022]    Functionally, fuel passes from the manifold  16  into a fuel supply passage  28  that may be inside or outside the fuel injector body  62 . As the controller  18  receives the engine condition signal  50  and fuel signal  46 , the controller  18  sends the control input  88  to direct the control valve  30  into one of the three positions. In the first position, no substantial quantity of fuel passes into nozzle reservoir  44  to act against the check valve  36 . In the second position, the control valve  30  allows some fuel to pass through the fuel supply passage  28  into the nozzle reservoir  44 . However, partial restriction of fluid communication between the fuel supply passage  28  and tip supply passage  32  reduces pressures in the nozzle reservoir  44  and fuel injection rates from the nozzle portion  34 . Moving the control valve  30  to the third position reduces restrictions in fluid communication between the fuel supply passage  28  and tip supply passage  32  to increase pressure at the nozzle reservoir  44  and thus injection rate from the nozzle portion  34 .  
         [0023]    Using the poppet  66 , the fuel is essentially contained in the fuel reservoir  82  where the solenoid is at current level a and corresponding armature position “a”. To get the stable injection rate “a”, current level “b” is sent initially to the solenoid to move armature  86  to armature position b and current level “c” holds the armature  86  in position. As the armature  86  moves to position “b”, fuel passes from the fuel reservoir  82  into the tip supply passage  32 . However, the poppet  66  restricts fuel flow through the fuel reservoir  82  and reduces fuel pressure. Fuel from the tip supply passage  32  builds pressure in the nozzle reservoir  44 . Fuel applies force to the check valve  36  near the head portion  38  causing the check valve  36  to act against the spring  45  and move the tip portion away from the seating portion  42  of the nozzle portion  34 .  
         [0024]    To create the ramp injection rate “b”, the current level “b” is sent to the solenoid  84  to move the armature  86  from either position “a” or position “b” to position “c”. Fuel flows from the supply passage  28  through the fuel reservoir  82  into the tip supply passage  32  with less restriction to flow than exhibited where the armature  86  is in position “b”. Again fuel applies force to the check valve  36  to move the tip portion  40  away from the seating portion  42 . Due to reduced restrictions, fuel pressures experienced at the tip portion  40  are greater and result in the ramp injection rate b.  
         [0025]    Using the control valve  30  to restrict flow between the fuel supply passage  28  and tip supply passage  32  allows a fuel injector  20  to perform various injection patterns without using two control valves. Adding the flow restriction  37  in the tip supply passage allows further control of fuel injection. Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.