Patent Publication Number: US-2002008154-A1

Title: Method and apparatus for providing a controlled injection rate and injection pressure in fuel injector assembly

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates, generally, to a method and apparatus for controlling the injection rate and injection pressure in an electromagnetic fuel injector. More specifically, the present invention relates to a method and fuel injector assembly for an internal combustion engine wherein the injection rate and injection pressure may be adjusted by varying the current to the solenoid actuated control valve to improve the operational characteristics of the fuel injector.  
       [0003] 2. Description of the Related Art  
       [0004] Fuel injector assemblies are employed in internal combustion engines for delivering a predetermined, metered mixture of fuel and air to the combustion chamber at preselected intervals. In the case of compression ignition, or diesel engines, the fuel/air mixture is delivered at relatively high pressures. Presently, conventional injectors are delivering this mixture at pressures as high as 32,000 psi. These are fairly high pressures and have required considerable engineering attention to ensure the structural integrity of the injector, good sealing properties, and the effective atomization of the fuel within the combustion chamber. However, increasing demands on greater fuel economy, cleaner burning, fewer emissions and NO x  control have placed, and will continue to place even higher demands on the engine&#39;s fuel delivery system, including increasing the fuel pressure within the injector.  
       [0005] Fuel injectors presently employed in the related art typically include a high pressure fuel passage which extends between a solenoid actuated control valve and the plunger cylinder in the injector body. Fuel at relatively low pressure is supplied to the control valve which then meters the delivery of the fuel at very high pressures and at predetermined intervals through the high pressure fuel passage to the plunger cylinder. The fuel ultimately exits the injector through a fuel nozzle.  
       [0006] The solenoid actuated control valve is supported in a stepped bore which typically extends through a side body of the injector. The stepped bore defines a supply chamber and a valve bore which receives a valve stem of the associated control valve. The valve bore terminates in a chamfered valve seat. Similarly, the valve stem terminates in a head which seats against the valve seat under the force generated by the solenoid. The head is configured to mate closely with the valve seat. At least a portion of the valve stem is subject to the high pressure generated in a valve opening direction during an injection cycle. Accordingly, the solenoid must generate sufficient force in the valve closing direction to overcome such pressure. These forces are borne by the valve seat through the head of the control valve.  
       [0007] While the design and operation of fuel injectors have continued to progress, there remains a constant need to improve fuel economy and reduce emissions while at the same time reducing engine noise induced from the operation of the fuel injector.  
       SUMMARY OF THE INVENTION AND ADVANTAGES  
       [0008] The present invention results in improvements over the design and operation of fuel injectors of the related art. More specifically, the present invention is directed toward an electromagnetic fuel injector assembly for an internal combustion engine. The fuel injector assembly includes an injector body having a control valve in fluid communication with a source of fuel for metering predetermined quantities of fuel to a nozzle assembly. The control valve is supported within a valve bore in the injector body and includes a solenoid connected to a source of electrical current and a valve member operatively connected to the solenoid and subject to the pressures developed in the injector for moving the valve member against a biasing force between an open and closed position. The valve bore includes a relieved portion. The solenoid is subject to reduced current from the source of electrical current at preselected times during the injection event to slightly unseat the valve in response to forces acting on the valve member in the valve opening direction to regulate the injection pressure and the injection rate of the fuel injector assembly. Alternatively, the head of the valve member may include a relieved portion which results in a reduced surface area contact between the head and the valve seat. This functions in the same manner as the relieved portion on the valve bore.  
       [0009] Additionally, the present invention is directed toward a method of controlling the injection rate and injection pressure of an electromagnetic fuel injector assembly. The method includes the steps of providing a first level of current to the solenoid for moving the valve member from an open to a closed position allowing the pressure in the injector to rise. Additionally, the method includes the steps of providing a reduced level of current to the solenoid at preselected times during the injection event to unbalance the forces acting on the valve member thereby slightly unseating the valve member to regulate the injection pressure and injection rate of the fuel injector. Finally, the method includes the steps of ending current to the solenoid and moving the valve member to its open position.  
       [0010] One advantage of the present invention is that a method and fuel injection assembly is provided which controls the injection rate and injection pressure of an electromagnetic fuel injector assembly. More specifically, the length of time and the level of current directed to the solenoid during the regulation modes determines the level of pressure regulation and the duration of the regulation. Another advantage of the present invention is that by increasing current to the solenoid at any time, valve sealing can be reestablished to resume traditional injection function.  
       [0011] Another advantage of the present invention is that by controlling the initial injection rate in diesel engines, the initial combustion rates may be reduced to lower engine noise or reduce NO x , emissions.  
       [0012] Still another advantage of the present invention is that by regulating the maximum injection pressure, the cam and plunger associated with the injector assembly may be sized to provide high injection pressures at low speed and load thereby improving fuel economy and reducing soot formation while, at the same time, preventing excessive structural loads at higher speeds and loads through the pressure regulation function.  
       [0013] Still another advantage of the present invention is that the depressurization rate of the fuel injector may be controlled. More specifically, reducing the depressurization rate or spill rate reduces the mechanical induced engine noise caused by the rapid unloading of the drive system. This feature is achieved by the present invention through lowering the current to the solenoid at the end of the injection event thereby slightly unseating the valve member prior to fully terminating the current to the solenoid. By regulating the current to the solenoid at the end of the injection event, the accelerating forces acting on the valve member in the valve opening direction may be reduced resulting in a reduced depressurization rate. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014] Other advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
     [0015]FIG. 1 is a partial cross-sectional side view of an electromagnetic fuel injector;  
     [0016]FIG. 2A is a partial cross-sectional side view of a conventional valve member of a solenoid actuated control valve for an electromagnetic fuel injector;  
     [0017]FIG. 2B is an enlarged partial cross-sectional side view of the valve member illustrated in FIG. 2A.  
     [0018]FIG. 2C is a partial cross-sectional side view of a valve member of a solenoid actuated control valve of the present invention illustrating the relieved portion in the valve bore thereof;  
     [0019]FIG. 2D is an enlarged, partial cross-sectional side view of the valve member of FIG. 2C;  
     [0020]FIG. 2E is a partial cross-sectional side view of a valve member of a solenoid actuated control valve of the present invention illustrating the relieved portion on the head of the valve member thereof;  
     [0021]FIG. 2F is an enlarged, partial cross-sectional side view of the valve member of FIG. 2E; and  
     [0022]FIG. 3 is a graphical depiction of the movement of the control valve as a function of solenoid current with reference to the injection pressure over time. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)  
     [0023] Referring now to FIG. 1, there is generally shown at  10  an electromagnetic fuel injector of the type commonly employed in injectors with an internal combustion engine wherein fuel is injected into a plurality of cylinders where it is combusted to generate power to rotate a crank shaft. More specifically, a fuel injector pump assembly  10  is shown in FIG. 1 having an electromagnetically actuated, pressure balanced control valve incorporated therein to control fuel discharge from the injector portion of this assembly  10  into a cylinder of the engine (not shown) in a manner to be described. As illustrated in this figure, the electromagnetic fuel injector assembly  10  includes an injector body  12  which has a vertical main body portion  14  and a side body portion  16 . The main body portion  14  includes a stepped, cylindrical bore  20  therethrough. The stepped, cylindrical bore  20  includes a cylindrical lower wall  22  which slidably receives a pump plunger  24 . In addition, the stepped, cylindrical bore  20  includes an upper wall  26  of larger internal diameter to slidably receive a plunger actuator follower  28 . The plunger actuator follower  28  extends out one end of the main body  14  whereby it and the pump plunger  24  connected thereto are adapted to be reciprocated by an engine driven cam or rocker as conventionally known in the art. A stop pin (not shown) extends through an upper portion of the main injector body portion  14  into an axial groove in the plunger actuator follower  28  to limit upward travel of the follower induced under the bias of a plunger return spring  34 .  
     [0024] A nut, generally indicated at  36 , is threaded to the lower end of the main body portion  14  and forms an extension thereof. The nut  36  has an opening  38  at its lower end through which extends the lower end of a combined injector valve body or nozzle assembly, generally indicated at  40 . The nozzle assembly  40  includes a spray tip  42 . The nozzle assembly  40  may include a number of elements which are all well known in the art and which form no part of the present invention. Accordingly, the inner workings of the nozzle assembly  40  will not be described in detail here.  
     [0025] The delivery of fuel from a source such as a fuel tank to the nozzle assembly  40  is controlled by means of a solenoid actuated, pressure balanced valve, generally indicated at  44  in the side body portion  16 . The side body portion  16  is provided with a stepped vertical valve bore, generally indicated at  46 , which defines a supply chamber  48  and an intermediate or valve stem guide portion  50 . The guide portion  50  of the valve bore  46  terminates in a valve seat  52 . The valve seat  52  is chamfered so as to define an angle relative to the centerline of the valve bore  46 . The valve  44  is received within the stepped vertical valve bore  46  and includes a valve member having valve stem  60  terminating in a head  54  which seats against the valve seat  52 . The stem  60  extends upward from the head  54 . A closure cap  56  is mounted to the underside of the side body portion  16  and in connection therewith forms a spill chamber  58 . The valve  44  is normally biased in a valve opening direction, downward with reference to FIG. 1, by means of a coil spring  62  which loosely encircles valve stem  60 . One end of the spring  62  abuts against a washer-like spring retainer  64  encircling the valve stem portion  60 . The other end of the spring  62  abuts against the lower face of a spring retainer  66 . Movement of the valve  44  in the valve closing direction, upward with reference to FIG. 1. is effected by means of a solenoid assembly, generally indicated at  68 . The solenoid assembly  68  includes an armature  70  having a stem  72  depending centrally from its head. The armature  70  is secured to the valve  44 .  
     [0026] As commonly known in the art, the solenoid assembly  68  may further include a stator assembly having an inverted cup shaped solenoid case  74 . A coil bobbin supporting a wound solenoid coil and a segmented multi-piece pole piece are typically supported within the solenoid case  74 . The solenoid coil is connected through electrical connectors  76  to a suitable source of electrical power via a fuel injection electronic control circuit (not shown). Thus, the solenoid coil can be energized as a function of the operating conditions of an engine as will be described in greater detail below.  
     [0027] A high pressure fuel passage, generally indicated at  78 , provides fluid conmmunication between the control valve  44  and the fuel nozzle assembly  40 . As shown in FIG. 1, the fuel passage  78  is formed by drilling a hole from one side of the side body portion  16  of the injector body  12  and between control valve  44  and the stepped cylindrical bore  20 . In this way, the fuel passage  78  defines a delivery portion  80  extending between the control valve  44  and the stepped cylindrical bore  20  and a stub portion  82  extending between the valve stem guide portion  50  in the control valve  44  and the side body portion  16 . A plug  84  seals the open end of the stub portion  82  of the high pressure fuel passage  78 . As illustrated in FIG. 1, the valve member including the valve stem  60  and at least a portion of the head  54  are subject to the high pressure via the delivery portion  80  of the fuel passage  78  developed by the injector. Thus, when energized, the solenoid assembly  68  moves the valve member to the closed position against the biasing force of the spring  62  and the pressures acting on the valve member via the fuel passage  78 .  
     [0028] Referring now to FIGS.  2 A-B, a conventional valve member movably supported in the guide portion  50  of the valve bore  46  is disclosed. The head  54  of the valve member is held against the valve seat  52  and against forces acting on the valve in the valve opening direction by the solenoid assembly  68 . However, as shown in FIGS.  2 C-E, the guide stem portion  50  of the valve bore  46  may include a relieved portion  86  which is subject to the pressures developed in the injector to provide forces acting on the valve member in the valve opening direction. Alternatively, as shown in FIGS.  2 E-F, the head  54  of the valve  44  may include a relieved portion  90  which results in reduced surface area contact between the head  50  and the valve seat  52 . Either of the relieved portions  86  on the guide stem portion  50  of the valve bore  46  or the relieved portion  90  on the head  54  of the valve member may be employed to balance the control valve  44  in the following manner.  
     [0029] During any given injection event, the solenoid assembly  68  may be subject to reduced current from the source of electrical current at preselected times to slightly unseat the valve member in response to the forces acting on the valve member in the valve opening direction and, in this way, to regulate the injection pressure and injection rate of the fuel injector. More specifically, and referring now to the graphs of FIG. 3, the movement of the control valve  44  as a function of the solenoid current is illustrated with reference to the injection pressure over time. As noted above, initiation of current at  92  supplied to the solenoid moves the control valve  44  in the valve closing direction as indicated at  94 . The pressure in the injector begins to rise as shown at  96 . Employing the method and apparatus of the present invention, during the initiation of the injection pressure. the current to the solenoid may be reduced at  98  to slightly unseat the valve member represented at  100  thereby controlling the rate of injection of the fuel as indicated at  101 . The current to the solenoid may then be increased again as indicated at  102  thus moving the valve member to its closed position as indicated at  104 .  
     [0030] Thereafter, when the pressure in the injector approaches the peak injection pressure as indicated at  106 , the level of current to the solenoid may be reduced as indicated at  108  to slightly unseat the valve member as indicated at  110  thereby regulating the maximum pressure in the injector. At the end of the injection cycle, the level of current to the solenoid may again be reduced as indicated at  112  to slowly unseat the valve assembly shown at  114  thereby controlling depressurization of the injector as indicated at  116 . More specifically, the rate of depressurization at  116  is slowed when compared with the depressurization of conventional injectors shown in dotted lines at  118 . Finally, once the injection event is completely over, the current to the solenoid is ended thereby moving the valve member to its open position under the influence of the spring  62  and any pressure existing in the fuel passage  78 .  
     [0031] In this way, the injection rate and injection pressure in the electromagnetic fuel injector assembly may be controlled. The length of time and the level of current directed to the solenoid during the regulation modes determines the level of pressure regulation and the duration of the regulation. However, by increasing current to the solenoid at any time, valve sealing can be reestablished to resume traditional injection functions. Additionally, by controlling the initial injection rate in diesel engines, the initial combustion rates may be reduced to lower engine noise or reduce NO x  emissions. Furthermore, by regulating the maximum injection pressure, the cam and plunger associated with the injector assembly may be sized to provide high injection pressures at low speed and load thereby improving fuel economy and reducing soot formation while, at the same time, preventing excessive structural loads at higher speeds and loads through the pressure regulation function. Finally, the depressurization rate of the fuel injector may also be accurately controlled. More specifically, by reducing the depressurization rate or spill rate, the mechanically induced engine noise caused by the rapid unloading of the drive system may be reduced. This feature is achieved by the present invention through lowering the current to the solenoid at the end of the injection event thereby slightly unseating the valve member prior to fully terminating the current to the solenoid. By regulating the current to the solenoid at the end of the injection event. the accelerating forces acting on the valve member in the valve opening direction may be reduced resulting in reduced depressurization rates.  
     [0032] The invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.  
     [0033] Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.