Abstract:
An improved fuel injector is provided which effectively controls fuel injection events using two injection control valves which operate in series to control the movement of a nozzle valve element. An outer injection control valve and actuator assembly operates to control fluid pressure in a control volume adjacent an inner injection control valve thereby controlling the movement of the inner control valve which, in turn, controls fuel pressure in an inner control volume adjacent one end of the nozzle valve element. A particular design of the inner injection control valve prevents control valve oscillations thereby minimizing unwanted fuel injection variations.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to an improved fuel injector which effectively controls fuel metering.  
         BACKGROUND OF THE INVENTION  
         [0002]    In most fuel supply systems applicable to internal combustion engines, fuel injectors are used to direct fuel pulses into the engine combustion chamber. A commonly used injector is a closed-nozzle injector which includes a nozzle assembly having a spring-biased nozzle valve element positioned adjacent the nozzle orifice for resisting blow back of exhaust gas into the pumping or metering chamber of the injector while allowing fuel to be injected into the cylinder. The nozzle valve element also functions to provide a deliberate, abrupt end to fuel injection thereby preventing a secondary injection which causes unburned hydrocarbons in the exhaust. The nozzle valve is positioned in a nozzle cavity and biased by a nozzle spring to block fuel flow through the nozzle orifices. In many fuel systems, when the pressure of the fuel within the nozzle cavity exceeds the biasing force of the nozzle spring, the nozzle valve element moves outwardly to allow fuel to pass through the nozzle orifices, thus marking the beginning of injection.  
           [0003]    In another type of system, such as disclosed in U.S. Pat. No. 5,819,704, the beginning of injection is controlled by a servo-controlled needle valve element. The assembly includes a control volume positioned adjacent an outer end of the needle valve element, a drain circuit for draining fuel from the control volume to a low pressure drain, and an injection control valve positioned along the drain circuit for controlling the flow of fuel through the drain circuit so as to cause the movement of the needle valve element between open and closed positions. Opening of the injection control valve causes a reduction in the fuel pressure in the control volume resulting in a pressure differential which forces the needle valve open, and closing of the injection control valve causes an increase in the control volume pressure and closing of the needle valve.  
           [0004]    U.S. Pat. No. 5,862,793 discloses an injection valve arrangement which includes a solenoid actuated control valve for controlling drain flow from a chamber, a poppet type needle valve movable outwardly to permit injection and an auxiliary valve positioned between the chamber and the needle valve for controlling high pressure fuel flow to a needle control chamber positioned adjacent an outer end of the needle valve. The opening of the control valve causes the opening of the auxiliary valve which then causes the opening of the needle valve. However, the auxiliary valve opens to allow high pressure fuel to enter the needle control chamber thereby increasing the pressure in the needle control chamber. The high pressure in the needle control chamber acts on the needle valve to move the needle valve outwardly into an open position to cause injection.  
           [0005]    There is still a need for a simple, improved fuel injector which is capable of effectively controlling fuel metering while handling high fuel injection flow rates using conventional actuators.  
         SUMMARY OF THE INVENTION  
         [0006]    It is, therefore, one object of the present invention to overcome the deficiencies of the prior art and to provide a fuel injector which better enables large engines to meet future diesel engine exhaust emission requirements while minimizing fuel consumption.  
           [0007]    Another object of the present invention is to provide a fuel injector which can be effectively used in high horsepower engines in combination with actuator assemblies used on smaller engines/injectors.  
           [0008]    Yet another object of the present invention is to provide a fuel injector for larger engines which avoids larger and higher energy consuming actuators and thus minimizes injector packaging and costs.  
           [0009]    Still another object of the present invention is to provide a fuel injector having a primary control valve and an intermediate control valve wherein oscillations of the intermediate valve are minimized.  
           [0010]    These and other objects are achieved by providing a fuel injector for injecting fuel at high pressure into the combustion chamber of an engine, comprising an injector body containing an injector cavity and an injector orifice communicating with one end of the injector cavity to discharge fuel into the combustion chamber. The injector also includes a nozzle valve element positioned in one end of the injector cavity adjacent the injector orifice and movable between an open position in which fuel may flow through the injector orifice into the combustion chamber and a closed position in which fuel flow through the injector orifice is blocked. The injector also includes a first control volume positioned to receive a pressurized supply of fuel, a drain circuit for draining fuel from the first control volume to a low pressure drain and a first valve seat positioned along the drain circuit. A first injection control valve is also positioned along the drain circuit to control fuel flow from the first control volume and includes a reciprocally mounted control valve member movable between an open position permitting flow through the drain circuit and a closed position in sealing abutment against the first valve seat to block flow through the drain circuit. A second control volume is also provided and positioned adjacent an outer end of the nozzle valve element to receive a pressurized supply of fuel while the drain circuit is positioned to drain fuel from the second control volume to the low pressure drain. A second valve seat is positioned along the drain circuit along with a second injection control valve to control fuel flow from the second control volume. The second injection control valve includes a reciprocally mounted control valve member movable between an open position permitting flow through the drain circuit to cause a decrease in fuel pressure in the second control volume and movement of the nozzle valve element into the open position, and a closed position in sealing abutment against the second valve seat to block flow through the drain circuit to cause an increase in fuel pressure in the second control volume and movement of the nozzle valve element into the closed position. Movement of the first injection control valve into the open position causes a decrease in fuel pressure in the first control volume thereby causing movement of the second injection control valve into the open position.  
           [0011]    The first injection control valve may include a solenoid actuator assembly while the second injection control valve is spring biased into the closed position. A high pressure chamber may be positioned around the second injection control valve axially between the first injection control valve and the second control volume. The second injection control valve includes a large diameter portion positioned axially between the first control volume and the high pressure chamber, and a small diameter portion having an outer diameter smaller than the large diameter portion and positioned axially between the high pressure chamber and the second control volume. The second injection control valve includes a bias spring positioned in the high pressure chamber for biasing the second injection control valve into the closed position. The nozzle valve element may include an outer diameter greater than the largest outer diameter of the second injection control valve member. The nozzle valve element moves toward the second injection control valve into the open position. A bias spring for biasing the nozzle valve element into the closed position may be provided. A spring chamber containing the nozzle valve bias spring may be provided along with a high pressure fuel supply circuit including at least a portion of the spring chamber. A high pressure fuel supply circuit may also include at least a portion of the high pressure chamber. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a cross sectional schematic view of the fuel injector of the present invention;  
         [0013]    [0013]FIG. 2 is a detailed cross sectional view of a practical embodiment of the fuel injector of FIG. 1;  
         [0014]    [0014]FIG. 3 a  is a detailed cross sectional view of a second practical embodiment of the fuel injector having a simplified inner control valve with fewer parts;  
         [0015]    [0015]FIG. 3 b  is an expanded view of a portion of the injector of FIG. 3 a ; and  
         [0016]    [0016]FIG. 4 a graph of nozzle valve element lift, first injection control valve lift, and second injection control valve lift versus time. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    Referring to FIG. 1, there is shown a closed nozzle fuel injector of the present invention, indicated generally at  10 , which functions to effectively permit accurate and reliable control of fuel metering during fuel injection into the combustion chamber of an internal combustion engine. Fuel injector  10  is especially advantageous in larger, high horsepower engines requiring greater fuel injection flow rates while avoiding the need for larger injection control valve and actuator assemblies and thus avoiding increased energy consumption and increased injector packaging dimensions.  
         [0018]    Fuel injector  10  generally includes an injector body  12  forming an injector cavity  14 . The lower portion of fuel injector body  12  includes a closed nozzle assembly, indicated generally at  16 , which includes a nozzle valve element  18  reciprocally mounted for opening and closing injector orifices  20  formed in body  12  thereby controlling the flow of injection fuel into an engine combustion chamber (not shown). A bias spring  22  is positioned in a spring chamber  24 , formed in injector cavity  14 , for abutment against a land formed on nozzle valve element  18  so as to bias nozzle valve element  18  into a closed position as shown in FIG. 1.  
         [0019]    A high pressure fuel supply circuit  26  is formed in injector body  12  for supplying high pressure fuel from a high pressure source, such as high pressure common rail  28 , to injector cavity  14 . Fuel injector  10  of the present invention may be adapted for use with a variety of fuel systems and high pressure fuel sources. For example, fuel injector  10  may receive high pressure fuel from high pressure common rail  28  or, alternatively, a pump-line-nozzle system or be modified to form a unit injector incorporating, for example, a mechanically actuated plunger into the injector body. Thus, fuel injector  10  of the present invention may be incorporated into any fuel system which supplies high pressure fuel to the injector while permitting the injector to control the timing and quantity of the fuel injected into the combustion chamber.  
         [0020]    The fuel injector  10  of the present invention further includes a first or outer injection control valve  30  positioned for controlling fuel flow from a first or outer control volume  32 , and a second or inner injection control valve  34  for controlling fuel flow from a second or inner control volume  36 . High pressure fuel circuit  26  delivers high pressure fuel to first and second control volumes  32 ,  36  while a drain circuit  38  directs fuel from first control volume  32  and second control volume  36  to a low pressure drain. An outer end of inner injection control valve  34  is positioned within first control volume  32  and exposed to fuel residing in volume  32 . Outer injection control valve  30  is positioned along drain circuit  38  to control fuel flow through drain circuit  38  so as to control the fuel pressure in first control volume  32 . Specifically, outer injection control valve  30  includes a reciprocally mounted control valve member  40  for engaging a first or outer valve seat  42  in a closed position in sealing abutment against first valve seat  42  to block flow through drain circuit  38  thereby permitting an increase in fuel pressure in first control volume  32 . Control valve member  40  is also movable, by for example, the energization of an actuator assembly  44 , into an open position against the bias force of a bias spring  46  to permit fuel flow through the drain circuit. A supply orifice  48  is positioned in a portion of high pressure fuel supply circuit  26  feeding first control volume  32  and designed with a smaller cross sectional flow area than drain circuit  38  and thus a greater amount of fuel is drained from first control volume  32  than is replenished via supply orifice  48 . As a result, the pressure in first control volume  32  decreases upon opening of control valve member  40 . Actuator assembly  44  may be any type of actuator assembly capable of selectively controlling the movement of control valve member  40 . For example, a fast proportional actuator, such as an electromagnetic, magnetostrictive or piezoelectric type, could be used to move control valve member  40 .  
         [0021]    Inner injection control valve  34  includes a reciprocally mounted control valve member  50  having an outer end positioned in first control volume  32  and an inner end positioned for sealing abutment against a second valve seat  52  when in a closed position. Second valve seat  52  is formed along drain circuit  38  so that positioning of control valve member  50  in the closed position blocks the drain flow of fuel from inner control volume  36  causing the pressure in control volume  36  to increase. A bias spring  54  is positioned to bias control valve member  50  into the closed position against second valve seat  52 . Control valve member  50  is also movable into an open position to allow fuel to drain from second control volume  36  through drain circuit  38  thereby decreasing the pressure in second control volume  36  due to a supply orifice  56  which functions in a similar manner to supply orifice  48 . Bias spring  54  is positioned in a high pressure chamber  58  positioned around inner injection control valve  34  and axially between outer injection control valve  30  and inner control volume  36 . High pressure chamber  58  receives high pressure fuel from high pressure fuel supply circuit  26  as shown in FIG. 1. The outer section of inner injection control valve  34  includes a large diameter portion  60  sized to form a close sliding fit with the opposing surface of injector body  12  thereby forming a partial fluid seal between high pressure chamber  58  and outer control volume  32 . Inner injection control valve  34  also includes a small diameter portion  62  having an outer diameter smaller than large diameter portion  60  and positioned axially between high pressure chamber  58  and inner control volume  36 . Likewise, small diameter portion  62  is sized to form a close sliding fit with the opposing bore surface of injector body  12  thereby creating a partial fluid seal separating inner control volume  36 /drain circuit  38  from high pressure chamber  58 . The significance of large diameter portion  60  and small diameter portion  62  on the operation of inner control valve  34  will be discussed hereinbelow.  
         [0022]    During operation, prior to an injection event, actuator assembly  44  of outer injection control valve  30  is de-energized causing control valve member  40  to be positioned in sealed abutment against outer valve seat  42  by the bias force of spring  46 . As a result, the fuel pressure level in outer control volume  32  is substantially the same as the fuel pressure level in fuel supply circuit  26 . Thus, high fuel pressure forces are imparted on the outer end of large diameter portion  60  of inner injection control valve  34  by the fuel in outer control volume  32  which, in combination with the bias force of spring  54  maintain inner control valve  34  in its closed position. Thus, the total closing forces acting on inner injection control valve  34 , including fuel pressure forces acting on the outer end of valve  34  in outer control volume  32  and the bias force of bias spring  54 , are greater than the fuel pressure forces tending to open inner control valve  34 . As a result, as shown in FIG. 1, control valve member  50  of inner control valve  34  is maintained in the closed position against inner valve seat  52  thereby blocking flow through drain circuit  38 . Thus, the fuel pressure level in inner control volume  36  is also at the pressure level of the fuel supply circuit  26 . The high pressure forces acting on the outer end of needle valve element  18 , in combination with the closing bias force of spring  22 , maintain needle valve element  18  in its closed position blocking flow through injector orifices  20 . High pressure fuel supply circuit  26  may include a supply passage  27  formed in needle valve element  18  for delivering high pressure fuel from spring chamber  24  to a lower nozzle cavity  29  for further delivery to the combustion chamber via orifices  20  when needle valve element  18  moves from the closed to the open position. At a predetermined time during the supply of high pressure fuel to high pressure fuel supply circuit  26 , actuator assembly  44  of outer injection control valve  30  is energized to controllably move control valve member  40  from the position shown in FIG. 1 outwardly to an open position permitting fuel flow from outer control volume  32  through drain circuit  38  to a low pressure drain. Simultaneously, high pressure fuel flows from high pressure fuel supply circuit  26  through supply orifice  48  into outer control volume  32 . However, orifice  48  is designed with a smaller cross sectional flow area than the portion of drain circuit  38  upstream of outer valve seat  42  and thus a greater amount of fuel is drained from outer control volume  30  than is replenished via supply orifice  48 . As a result, the pressure in outer control volume  30  immediately decreases. Upon a sufficient decrease in the fuel pressure forces acting on the outer end of control valve member  40  in outer control volume  32 , the fuel pressure forces tending to open inner injection control valve member  34  become larger than the fuel pressure forces acting on control valve member  50  in outer control volume  32  in combination with the bias force of spring  54  to thereby move control valve member  50  outwardly from the closed position into an open position. Specifically, by designing small diameter portion  62  with a smaller diameter than large diameter portion  60  of control valve member  50 , and including high pressure chamber  58  having a pressure level equal to the pressure level in fuel supply circuit  26 , the point at which control valve member begins to open during the decrease of fuel pressure in inner control volume  32  can be controlled while also ensuring that control valve member  50  is maintained in the open positioned in a controllable manner without oscillations while in the open position. A difference in diameter between small diameter portion  62  and large diameter portion  60  creates greater opening forces on control valve member  50  thereby avoiding the undesirable oscillations. As the outer end of control valve member  50  approaches the outer face of outer control volume  32  and tends to block the flow from drain circuit  38 , the fuel pressure in outer control volume  32  tends to increase. In prior conventional control designs, this tendency causes control valve member  50  to move back toward the closed position thereby initiating cyclical pressure variations in the outer control volume once again. The cyclical pressure variations result in an oscillating movement of prior conventional control valve members toward open and closed positions which interferes with fuel injection controllability. The design of the present invention avoids this oscillating effect thereby improving the controllability of the fuel injection event.  
         [0023]    Upon the opening of inner injection control valve  34 , high pressure fuel flows from inner control volume  36  through drain circuit  38 . Simultaneously, high pressure fuel flows from high pressure fuel supply circuit  26  through orifice  56  into inner control volume  36 . However, orifice  56  is designed with a smaller cross sectional flow area than drain circuit  38  upstream of second valve seat  52  and thus a greater amount of fuel is drained from inner control volume  36  than is replenished via orifice  56 . As a result, the pressure in inner control volume  36  immediately decreases. Fuel pressure forces acting on needle valve element  18  due to high pressure fuel in lower nozzle cavity  29  begins to move needle valve element  18  outwardly from the closed position shown in FIG. 1 toward an open position. Thus, the difference in diameters between large diameter portion  60  and small diameter portion  62  and the use of high pressure chamber  58  containing high pressure fuel for acting on the surfaces creating the forces tending to move control valve member outwardly, enables control valve member  50  to reach an equilibrium position permitting a small amount of drain flow from outer control volume  32  to compensate for the charge flow entering control volume  32  so as to automatically maintain control valve member  50  in its open position without oscillations.  
         [0024]    Fuel injector  10  of the present invention is especially advantageous in high horsepower engines requiring a larger amount of fuel for injection during each injection event. Nozzle valve element  18  of fuel injector  10 , when applied to a high horsepower engine, includes greater needle lift, increased injector orifice size and a larger nozzle valve element seat diameter to meet the larger fuel injection demand. As a result, the nozzle valve element is designed with a larger outer diameter than conventional nozzle valve elements resulting in a larger inner control volume  36 . In conventional injectors used in high horsepower engines which do not include an inner injection control valve, a larger and more powerful actuator assembly is required to control the flow from the larger control volume adjacent the nozzle valve element thereby resulting in increased component costs, energy consumption and packaging difficulties. Fuel injector  10  of the present invention avoids the use of a larger actuator assembly and permits conventional smaller less energy consuming actuator assemblies typically used on medium horsepower engines to be used on high horsepower engines while effectively controlling the movement of the nozzle valve element thereby providing accurate and reliable control over fuel injection events.  
         [0025]    [0025]FIG. 2 discloses a cross sectional view of a practical embodiment of the same injector as FIG. 1 with like components referred to with the same reference numbers as used in FIG. 1. Injector body  12  specifically includes a lower nozzle housing  100 , an upper nozzle housing  102 , a spacer  104 , a barrel  106  and a retainer  108 . These components are held in compressive abutting relationship in the interior of retainer  108 . For example, the outer end of retainer  108  may contain internal threads  110  for engaging corresponding external threads on barrel  106  to permit the entire injector body  12  to be held together by simple relative rotation of retainer  108  with respect to barrel  106 . In this embodiment, nozzle valve element  18  may include two integral delivery passages  27  for directing flow past two guide portions of the nozzle valve element and into lower nozzle cavity  29 . The outer portion of nozzle valve element  18  is positioned within a sealing sleeve  112  comprised of a lower sleeve portion  114  and an upper sleeve portion  116  which are held in sealed compressive abutting relationship by the bias force of spring  22 . The inner control volume  36  is formed in upper sleeve portion  116  and drain circuit  38  includes an axial passage extending through upper sleeve  116  and spacer  104 . High pressure fuel supply circuit  26  includes a supply port  118  formed in the side of upper sleeve  116 . As can be seen from FIG. 2, inner injection control valve  34  is positioned in a bore formed in barrel  106 . The outer portion of control valve member  50  extends into a two part sleeve, indicated generally at  120 , in a similar manner to sleeve  112 . Bias spring  54  abuts the inner end of sleeve  34  to maintain the two part sleeve in position. Likewise, a supply port  122  supplies fuel from high pressure fuel supply circuit  26  into outer control volume  32  formed in sleeve  34 . Outer injection control valve  30  is mounted on fuel injector body  12  via a connector sleeve  124  which threadably engages the outer injection control valve body and barrel  106 . As with the schematic illustration of FIG. 1, actuator assembly  44  may be a solenoid operated, two-way valve including control valve member  40  biased into the closed position by bias spring  46 . The details of first injection control valve  30  are shown in FIG. 2; however, a similar injection control valve, disclosed in U.S. Pat. No. 6,056,264, the entire contents of which is hereby incorporated by reference, may be used.  
         [0026]    The specific practical embodiment shown in FIG. 2 operates in substantially the same manner as the schematic showing of FIG. 1 as described hereinabove. Also, the advantages of the schematic showing of the present invention in FIG. 1 as described hereinabove equally apply to the specific embodiment of FIG. 2.  
         [0027]    [0027]FIGS. 3 a  and  3   b  disclose cross sectional views of a second practical embodiment of the same injector as FIG. 1 with like or similar components referred to with the same reference numbers as used in FIG. 1. Injector  200  of FIGS. 3 a  and  3   b  specifically includes an injector body  202  including a lower nozzle housing  204 , an upper nozzle housing  206 , a spacer  208 , a barrel  210 , a first retainer  212  and a second retainer  214 . These components are held in compressive abutting relationship by retainers  212  and  214 , the ends of which threadably engage threads formed on the outer surface of the injector body to permit the body to be held together by simple relative rotation of the retainers with respect to the other components. The injector of FIGS. 3 a  and  3   b  is of course also very similar to the injector of FIG. 2 with like components referred to with the same reference numbers as used in FIG. 2. The primary distinction between the present embodiment of FIGS. 3 a  and  3   b  and the previous embodiment of FIG. 2 is that the inner injection control valve  34  is a more simplified design including barrel  210  and single piece control valve member  216 . It is noted that no bias spring is provided for inner injection control valve  34  since during normal operation the bias spring is not needed. During shutdown, the supply pressure provided to outer control volume  32  is sufficient to hold control valve member  216  in the closed position. If there is no pressure in the supply passage  26 , for example during extended shutdown, leakage past inner injection control valve  34  to drain is acceptable. Upon startup, any pressure buildup in the fuel supply passage would immediately hold control valve member  216  closed. It should be noted that supply fuel is delivered to outer control volume  32  via high pressure supply circuit  26  which includes a transverse passage  218  (FIG. 3 b ) formed in control valve member  216 . Also, the supply orifice  48  is located in the top end of passage  218  formed in control valve member  216 . It should also be noted that although no bias spring is used in the preferred embodiment as shown, a bias spring may be included and positioned in outer control volume  32 . The plunger stroke length of control valve member  216  of inner injection control valve  34  is set by grinding the member  216  to the predetermined length prior to assembly. The specific practical embodiment shown in FIGS. 3 a  and  3   b  operates in substantially the same manner as the schematic shown in FIG. 1 as described hereinabove. Also, the advantages of the schematic showing of the present invention in FIG. 1 as described hereinabove equally apply to the specific embodiment of FIGS. 3 a  and  3   b.    
         [0028]    As illustrated in FIG. 4, the injection control valves and nozzle valve element open and close in sequence or series with the outer or first injection control valve  30  first opening followed by the opening of inner or second injection control valve  34  which then causes the opening of nozzle valve element  18 . At the end of the injection event, outer injection control valve  30  is closed followed by the closing of inner injection control valve  34  which then causes nozzle valve element  18  to close. As the graph of FIG. 4 illustrates, a minimal delay of 50-80 microseconds exists between the operation of the inner and outer injection control valves  30 ,  34  respectively.  
       INDUSTRIAL APPLICABILITY  
       [0029]    It is understood that the present invention is applicable to all internal combustion engines utilizing a fuel injection system and to all closed nozzle injectors including unit injectors. This invention is particularly applicable to diesel engines which require accurate fuel injection control by a simple control device and, in particular, high horsepower diesel engines. Such internal combustion engines including a fuel injector in accordance with the present invention can be widely used in all industrial fields, commercial and noncommercial applications, including trucks, passenger cars, industrial equipment, stationary power plants and others.