Abstract:
A fuel injector that includes a sliding armature, decoupled armature, or flying armature movable between a pintle stop and a housing stop. Flying armatures are generally used to increase the total force applied to the pintle stop for lifting the pintle off a nozzle seat to open the fuel injector. When the fuel injector is turned off, a housing stop is arranged to absorb kinetic energy present in the flying armature so that the kinetic energy is not imparted to the nozzle seat.

Description:
TECHNICAL FIELD OF INVENTION 
     The invention generally relates to a fuel injector, and more particularly relates to reducing the occurrence of pintle bounce back when the fuel injector is turned off to stop fuel from flowing from the fuel injector. 
     BACKGROUND OF INVENTION 
     Many electro-magnetic type fuel injectors are configured such that when a current is applied to a coil winding within the fuel injector, a magnetic field is generated that urges the pintle/ball assembly away from the nozzle seat and thereby turns the injector ON. In general, the amount of force needed to lift a pintle/ball assembly from the injector OFF or closed position to the injector ON or open position is proportional to a pintle return spring force plus a fuel pressure of the fuel present in the injector. However, some direct injection fuel systems have increased fuel pressures to a level where it becomes difficult to provide a fuel injector that has the same physical outline or package size as injectors designed for lower fuel pressure levels, and is able to reliably ‘dead lift’ the pintle/ball assembly at the higher fuel pressure levels. 
     It has been proposed to add a sliding armature, also known as a decoupled armature or flying armature, that in response to the magnetic field, accelerates towards and strikes a pintle stop like a slide hammer to provide a combination of kinetic energy and static force to lift the pintle/ball assembly off the nozzle seat. However, the additional mass of this armature undesirably increases the impact force of the pintle/ball assembly on the nozzle seat when the fuel injector is turned OFF, which may lead to the ball bouncing back off the nozzle seat, thereby resulting in unmetered fuel being dispensed, or fuel being dispensed that is not properly atomized. This temporary movement of the pintle/ball away from the seat may also be referred to as pintle bounce. Elimination or reduction of this unmetered fuel may also reduce injector to injector flow variation. The increased impact force may also lead to undesirable noise and/or reduced injector life. 
     SUMMARY OF THE INVENTION 
     The invention described herein provides a housing stop to absorb kinetic energy from a sliding armature when a fuel injector is being turned off. 
     In accordance with one embodiment of this invention, a fuel injector includes a housing, a nozzle seat, a pintle, a pintle stop, a housing stop, and a sliding armature. The housing is configured to direct fuel flow therethrough. The nozzle seat is fixedly coupled to the housing and configured to direct fuel flow from the fuel injector. The pintle is arranged within the housing. The pintle is movable to an open position where the pintle is spaced apart from the nozzle seat such that fuel is dispensed by the fuel injector and a closed position where the pintle contacts the nozzle seat such that no fuel is dispensed by the fuel injector. The pintle stop is fixedly coupled to the pintle. The housing stop is fixedly coupled to the housing. The sliding armature movable between the pintle stop and the housing stop in response to a magnetic field. When the magnetic field is present, the sliding armature contacts the pintle stop and urges the pintle toward the open position. When the magnetic field is not present, the pintle is free to move toward the closed position. The sliding armature is separated from the pintle stop when the sliding armature contacts the housing stop. 
     Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will now be described, by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  is cross sectional view of a fuel injector in accordance with one embodiment; 
         FIG. 2  is a close-up view showing details of the fuel injector in  FIG. 1  at different operating conditions; and 
         FIG. 3  is a close-up view of a prior art fuel injector. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     In accordance with an embodiment of a fuel injector for an internal combustion engine,  FIGS. 1-2  illustrate a fuel injector  10 . In general, the injector  10  has a pintle  12  that may include a ball  14  or other feature configured to cooperate with a nozzle seat  16  to regulate the flow of fuel in cavity  18 , hereafter fuel  18 , to be dispensed by the injector  10 .  FIG. 2A  shows the pintle  12  after moving into a closed position that positions the ball  14  in contact with the nozzle seat  16  to prevent fuel  18  from flowing out of injector  10 .  FIG. 2B  shows the pintle  12  after moving into an open position so the ball  14  can be apart from the nozzle seat  16  to allow fuel  18  to be dispensed by the fuel injector  10 . 
     The injector  10  may also include a sliding armature  20  movable between a first position against a housing stop  22  as illustrated in  FIG. 2A , and a second position against an armature stop  24  as illustrated in  FIG. 2B . As will be explained in more detail later, the sliding armature  20  may be urged toward the armature stop  24  by a magnetic field that is generally directed toward or through at least a portion of the sliding armature  20  for moving the sliding armature  20  toward the armature stop  24 . The sliding armature  20  may be slideably coupled to the pintle  12  as illustrated in  FIGS. 2A and 2B  where the sliding armature  20  surrounds a portion of the pintle  12  and slides along that portion. The pintle  12  and the sliding armature  20  may be configured so that the sliding armature  20  contacts a pintle stop  28  as the sliding armature  20  moves from a position near the housing stop  22  toward the armature stop  24 . If the sliding armature  20  is being urged toward the armature stop  24 , then the contact with the pintle stop  28  will act to urge the pintle  12  toward the open position. When the sliding armature  20  is against the armature stop  24 , then the pintle  12  is generally considered to be in the open position. The sliding armature  20  may also be slideably coupled to the pintle  12  such that the pintle  12  is free to move to the closed position when the sliding armature  20  is not in contact with the armature stop  24  and the pintle stop  28  or when the sliding armature  20  is at or near the housing stop  22 . 
     The components described and illustrated as being within the injector  10  are generally enclosed in a housing  30  configured to support the components and direct fuel flow therethrough. The nozzle seat  16  is fixedly coupled to the housing  30  in a manner that seals to prevent fuel leakage and is generally configured to direct fuel flow from the fuel injector  10  in a particular spray pattern. The pintle stop  28  may be provided by a separate piece fixedly coupled to the pintle  12 , or may be formed integrally with the pintle  12 . Likewise, the housing stop  22  may be provided by a separate part such as a stop ring  34  as illustrated that is fixedly coupled to the housing, or may be a feature integrally formed with the housing  30 . The location of the housing stop  22  and the configuration of the stop ring  34  is selected so that the kinetic energy stored in the sliding armature  20  when the sliding armature is moving toward the housing stop  22  is transferred to the housing stop  22  instead of being transferred to the nozzle seat  16  as will be described in more detail below. 
     The arrangement of the sliding armature  20  and the armature stop  24  may define an air gap  32  having a gap size that depends on the position of the sliding armature  20  relative to the armature stop  24 . The housing  30  may also include a coil  40  configured to generate the magnetic field in response to a coil current arising from a voltage being applied to first and second connector pins  42 . While  FIG. 1  only shows one connector pin, it will be appreciate that at least two electrical connections are necessary to generate current in the coil  40 . 
     When a coil current through the coil  40  arises following the application of a voltage to the coil  40 , a magnetic field may be generated that urges the sliding armature  20  toward the armature stop  24 . When the sliding armature  20  makes contact with the pintle stop  28 , a static force arising from the magnetic field acting on the sliding armature  20  may act on the pintle  12  to urge it to the open position. In addition, when the sliding armature  20  makes contact with the pintle stop  28  while the armature is moving toward the armature stop  24 , an impact force arising from the kinetic energy of the sliding armature  20  at the moment of impact with the pintle stop  28  may combine cooperatively with the static force to generate a pintle opening force greater than either the static force or the impact force alone. Such a combination of forces may be effective to overcome a pintle closing force and thereby move the pintle  12  from the closed position to the open position. In other words, following the application of a coil current to the coil  40 , the impact of the sliding armature  20  on the pintle stop  28  acts like a slide hammer striking the pintle stop  28  to help overcome the forces holding the pintle  12  in the closed position. Further explanation of is found in U.S. patent application Ser. No. 12/821,475 by Mieney et al, filed Jun. 23, 2010, the entire disclosure of which is hereby incorporated herein by reference. 
     When the magnetic field is not present the pintle  12  is free to move toward the closed position, and the sliding armature  20  is separated from the pintle stop when the sliding armature contacts the housing stop  22 . While the sliding armature is moving toward the housing stop  22 , the sliding armature  20  has kinetic energy that must be dissipated to stop the motion of the sliding armature.  FIG. 3  shows a prior art fuel injector arrangement that, instead of transferring the sliding armature kinetic energy into a housing stop  22 , transfers that kinetic energy to the pintle  12  by way of a second pintle stop  36 . With this arrangement, the sliding armature kinetic energy will ultimately be transferred through the ball  14  into the nozzle seat  16 . It has been observed that such an arrangement can lead to reduced reliability due to accelerated wear of interface between the ball  14  and the nozzle seat  16 . It has also been observed that the transfer of kinetic energy to the nozzle seat  16  may cause the pintle  12  to bounce back and momentarily lift the ball  14  so that unmetered and/or insufficiently atomized fuel  18  is dispensed by the fuel injector  10 . 
     In one embodiment, the pintle closing force may be due solely to a fuel pressure of the fuel  18  acting on the pintle  12  and/or ball  14  to urge the pintle toward the closed position. In general, as the fuel pressure increases, the pintle closing force increases proportionately and so the force necessary to move the pintle  12  and/or ball  14  away from the closed position increases accordingly. In another embodiment, the pintle closing force may also include a spring force arising from a pintle spring  26  acting on the pintle to urge the pintle toward the closed position. It will be appreciated that for some pintle/ball/seat configurations the spring load of the pintle spring  26  may also need to increase as the fuel pressure increases to prevent leakage of the fuel  18  from within the fuel injector  10 . Also, the spring rate may be increased if a faster injector closing time is desired or if different spray performance is desired. In general, operating fuel pressures continues to move in the direction of higher pressures to improve spray atomization and practical flow range, and this may exacerbate pintle bounce. 
     In one embodiment, the fuel injector  10  may include an armature spring  44  configured to urge the sliding armature  20  toward the housing stop  22 . Including the armature spring is advantageous in that it assures that the sliding armature  20  is as far away from the pintle stop  28  when coil current to coil  40  is applied so that the sliding armature  20  as much distance as possible to accelerate before contacting the pintle stop  28 . The spring rate and preload of the armature spring  44  is selected by considering several aspects of desired fuel injector operating characteristics such as injector opening speed and vibration induced by the injector installation. 
     Accordingly, a fuel injector  10  capable of operating at higher fuel pressures and avoiding dispensing of unwanted or under-atomized fuel during an injector closing event is provided. The sliding armature  20  enables the fuel injector to be opened at higher fuel pressures without resorting to a larger injector assembly and/or higher coil currents. When the fuel injector  10  is attached to an internal combustion engine such as an automobile engine, kinetic energy present in the sliding armature  20  when the sliding armature is moving to allow the pintle  12  to move to the closed position is transferred through the housing  30  into the engine block or fuel injector mounting apparatus instead of being transferred to the nozzle seat  16  as is the case for some prior art configurations. Durability testing of fuel injectors having key features similar to those shown in  FIGS. 1-2  has indicated that both the Dynamic Flow Shift and Static Flow Shift induced by a durability test is reduced by about 50% when compared to fuel injectors having key features similar to those shown in  FIG. 3 . Dynamic Flow Shift is a measure of shift in fuel quantity delivered by an injector following a durability test when the injector is operated in a manner similar to what is expected when the injector is operating on an engine. Static Flow Shift is a measure of shift in fuel delivery rate following a durability test when the injector is held in the open state. Subsequent teardown of tested injectors exhibit wear characteristics consistent with the flow shifts. 
     While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.