Abstract:
The present invention provides a valve arrangement for metering fluid flow. The valve arrangement includes a valve seat including an orifice through which fluid flows. The valve arrangement also includes a valve displaceable along an axis between a first position contiguously engaging the valve seat and a second position spaced from the valve seat. Fluid flow between the valve seat and the valve is prevented in the first position and is permitted in the second position. The valve arrangement further includes a counterweight mounted on the valve for relative movement therebetween.

Description:
A CROSS REFERENCE TO RELATED APPLICATIONS 
     Continuity Statement This invention claims the benefit of the filing date of U.S. Provisional Application No. 60/214,747, filed Jun. 29, 2000, and incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF INVENTION 
     This invention relates to fuel injectors in general and particularly to fuel injectors for Compressed Natural Gas (CNG). More particularly, this invention relates to a damping system for counteracting rebound of a valve needle during the operation of a fuel injector. 
     Compressed natural gas, which is a common fuel for commercial fleet vehicles, is delivered to an engine through one or more fuel injectors. Each injector is required to deliver a precise amount of fuel per injection pulse, and maintain this precision over the life of the injector. In order to maintain this level of performance for an injector, certain strategies and sequences of operations are required to optimize the combustion of the fuel. 
     In order to promote efficient fuel consumption, the injector is required to open and close very quickly. This is effectively accomplished using a magnetic circuit to displace the valve needle with respect to an injector outlet seat. Specifically, a magnetic field—or flux—is produced relatively quickly across a working gap between a fuel inlet member, which acts as a stator, and an armature connected to the valve needle. A conventional magnetic circuit for an injector includes the inlet member, the armature, a valve body shell, a housing (providing a flux return path), and a coil. When energized, the coil produces the flux that is conducted through the steel parts of the magnetic circuit. The flux creates an attractive (or repulsive) force at the working gap, which moves the armature and valve needle, to open (or close) the injector. 
     However, quickly opening the injector creates a relatively severe impact between the armature and the inlet member. And quickly closing the injector creates a relatively severe impact between the armature needle assembly and injector outlet seat. In a CNG injector, the factors that affect the injector opening and closing impact velocities are more severe than in a gasoline injector. Compared to the gasoline injector, the CNG injector has two to three times more lift, less spring preload, and a similar force required to open the injector. These factors are exaggerated by the lower viscosity of CNG relative to gasoline. 
     The much greater lift of the CNG injector corresponds to the need for a much higher flow rate and area in order to obtain the same amount of energy flow through the injector for a given pulse. This is because CNG has a relatively lower density than gasoline. 
     The increased lift creates two problems. First, the increased lift substantially reduces the magnetic force available to open the injector. Second, the velocities created because of the longer flight times can be higher, creating higher impact momentum. The reduction in magnetic force also creates another problem: it is necessary to use a lighter spring preload than in a gasoline injector. 
     A conventional gasoline injector uses about four Newtons of spring preload and a very small gasoline force on the needle armature assembly while the injector is closed. In a CNG injector, the force of the gas pressure is about three Newtons and the force of the spring is about two Newtons. In operation, energizing a CNG or gasoline injector causes the needle armature to begin to move when the magnetic force reaches a level that overcomes the spring and the fuel force. However, in a CNG injector, the fuel force is removed as soon as the needle/seat seal is broken and the pressure equalizes at the tip of the needle. At this point, the magnetic force is substantially higher then it needs to be to lift the armature needle assembly against the force of the spring. This excess magnetic force, combined with a relatively light spring preload, high lift, and low viscosity CNG all contribute to high impact velocities between the armature and the inlet member. Lifting the needle also allows CNG to jet out through the injector outlet seat. To close the injector outlet, the magnetic coil is de-energized. In absence of the magnetic force, the armature needle assembly travels under the bias of the spring until the needle tip contacts the injector outlet seat, thereby closing the injector. The high velocity of the armature needle assembly that culminates in the closing impact between the needle tip and the injector outlet seat can cause the armature needle assembly to rebound, which can result in an uncontrolled secondary fuel injection(s). Thus, there is a need to provide fuel injectors (compressed natural gas injectors in particular) with mechanical damping for the armature needle assembly during opening and closing of the gaseous fuel valve. 
     SUMMARY OF THE INVENTION 
     The present invention provides a valve arrangement for metering fluid flow. The valve arrangement includes a valve seat including an orifice through which fluid flows. The valve arrangement also includes a valve displaceable along an axis between a first position contiguously engaging the valve seat and a second position spaced from the valve seat. Fluid flow between the valve seat and the valve is prevented in the first position and is permitted in the second position. The valve arrangement further includes a counterweight mounted on the valve for relative movement therebetween. 
     The present invention also provides a fuel injector for metering fuel flow to a combustion chamber of an internal combustion engine. The fuel injector includes a body having an inlet, an outlet, and a fuel flow passage extending along an axis between the inlet and the outlet. The fuel injector further includes a valve seat that is proximate to the outlet and an orifice through which fuel flows. The fuel injector also includes an armature assembly positioned in the passage and displaceable along the axis between first and second positions. The armature assembly includes a valve contiguously engaging the valve seat in the first position to prevent fuel flow through the orifice and spaced from the valve seat in the second position to permit fuel flow through the orifice. The armature assembly also includes a counterweight mounted for relative movement with respect to the armature assembly. 
     The present invention further provides a method of preventing uncontrolled fuel flow from a fuel injector having an inlet, an outlet, and a fuel flow passage extending along an axis between the inlet and the outlet. The method includes providing a valve seat proximate the outlet. The valve seat includes an orifice through which fuel flows. The method further includes providing an armature assembly displaceable along the axis between first and second positions. The armature assembly includes a valve contiguously engaging the valve seat in the first position to prevent fuel flow through the orifice and being spaced from the valve seat in the second position to permit fuel flow through the orifice. The method also includes mounting a counterweight on the armature assembly for relative movement therebetween. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention. 
     FIG. 1 is a cross-sectional view of a fuel injector according to the invention. The cross-section is taken along a longitudinal axis of the fuel injector. 
     FIG. 2 is an enlarged cross-sectional view of the body of the fuel injector shown in FIG. 1, which illustrates the motion damper of the present invention; 
     FIG. 3 is a perspective view of the motion damper illustrated in FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a fuel injector  10 , which can be a high-pressure, direct-injection fuel injector. The fuel injector  10  has a housing, which includes a fuel inlet  12 , a fuel outlet  14 , and a fuel passageway  16  extending from the fuel inlet  12  to the fuel outlet  14  along a longitudinal axis  18 . The housing includes an overmolded plastic member  20  cincturing a metallic housing member  22 . 
     The overmolded plastic member  20  also cinctures a fuel inlet member  24  having an inlet passage  26 . The inlet passage  26  serves as part of the fuel passageway  16  of the fuel injector  10 . A fuel filter  28  can be provided in the inlet member  24 . An adjustable tube  30  is positionable along the longitudinal axis  18 , before being secured with respect to the inlet member  24 , to vary the deflection (or compression) of an armature bias spring  32 , which contributes to controlling the quantity of fluid flow through the injector. The overmolded plastic member  20  also supports a socket  20 a that receives a plug (not shown) to operatively connect the fuel injector  10  to an external source of electrical potential, such as an electronic control unit ECU (not shown). An elastomeric O-ring  34  is provided in a groove on an exterior extension of the inlet member  24 . The O-ring  34  is supported by a back up washer  38  to sealingly secure the inlet member  24  with a fuel supply member, such as a fuel rail (not shown). 
     The metallic housing member  22  encloses a solenoid coil assembly  40 . The coil assembly  40  includes a bobbin  42  that retains a coil  44 . The ends of the coil  44  are electrically connected via the socket  20   a  of the overmolded plastic member  20 . An armature  46  reciprocates in the inlet passage  26  and is aligned along the axis  18  by a spacer  48 , a body shell  50 , and a body  52 . The armature  46  has an armature passage  54  that is aligned along the longitudinal axis  18  and in fluid communication with the inlet passage  26 . 
     The spacer  48  engages the body  52 , which is partially disposed within the body shell  50 . An armature guide  56  is located at an inlet portion  60  of the body  52 . An axially extending body passage  58  connects an inlet portion  60  of the body  52  with an outlet portion  62  of the body  52 . The armature passage  54  of the armature  46  is axially aligned with the body passage  58  of the body  52  along the longitudinal axis  18 . A seat  64  is located at the outlet portion of the body  62 . 
     The body  52  has a neck portion  66 , which is, preferably, a cylindrical annulus that surrounds a needle  68 . The needle  68  is fixed to the armature  46 , and is preferably, a substantially cylindrical needle  68 . The cylindrical needle  68  is centrally located within the neck portion  66  and is axially aligned with the longitudinal axis  18  of the fuel injector  10 . A damper  140  is slidingly provided on the needle  68 . The length L of the damper  140  is chosen such that when the needle  68  contacts the seat  64 , the downward motion of the damper  140  provides a second impact on stop surface  77  of needle tip  79 . Thus, an axial clearance  70  is provided between a top surface of the damper  140  and a stop surface  72  of the armature  46 , and/or a clearance  74  is provided between a bottom surface of the damper  140  and the stop surface  77  of needle tip  79 . As shown in FIG. 3, the damper  140  can include, but is not limited to a cylindrical cross-section. 
     In operation, an end of the armature  46  that is proximate to the fuel inlet member  24  is magnetically coupled to the adjustable tube  30 . A portion of the inlet member  24  that is proximate to the armature  46  serves as a stator for the magnetic circuit that is formed with the armature  46  and coil assembly  40 . The armature  46  is guided by the armature guide  56  and is responsive to an electromagnetic force generated by the coil assembly  40  for axially reciprocating the armature  46  along the longitudinal axis  18  of the fuel injector  10 . The electromagnetic force is generated by current flow from the ECU through the coil assembly  40 . Movement of the armature  46  also moves the attached needle  68  and the motion damper  140 . The needle  68  engages the seat  64 , which opens and closes the seat passage  76  of the seat  64  to permit or inhibit, respectively, fuel from exiting the outlet  14  of the fuel injector  10 . In order to open seat passage  76 , the seal between the needle  68  and the seat  64  is broken by upward movement of the needle  68 . The needle  68  moves upwards when the magnetic force is substantially higher than it needs to be to lift the armature needle assembly against the force of spring  32  and the pressure of the fuel in the injector  10 . This excess magnetic force, which increases exponentially as the armature  46  moves toward the inlet member  24 , combined with a relatively light spring preload, high lift, and low viscosity of CNG, all contribute to a high impact velocity between the armature  46  and the inlet member  24 . In order to close the seat passage  76  of the seat  64 , the magnetic coil assembly  40  is de-energized. In the absence of the magnetic force, the spring  32  preload and the low viscosity CNG both contribute to a high impact velocity between the needle  68  and the seat  64 , which can cause the armature needle  46  assembly to rebound, which can produce uncontrolled fuel injection(s). The motion damper  140  is provided to counteract rebound between the armature  46  and the inlet member  24  during valve opening, and to prevent the armature needle assembly from rebounding during the valve closing. For the seat passage  76  opening and the closing states, the motion damper  140 , which is slidingly or resiliently mounted on the needle  68 , absorbs the energy applied to armature  46  when the armature needle assembly contacts inlet member  24 , and when the curved surface  78  of needle  68  contacts conical end  80  of seat  64 . It should be noted that the damper  140  can be resiliently mounted to the needle  68  and/or the armature  46  by means of biasing elements (not shown), such as coil springs or rubber bumpers. These biasing elements (not shown) can be located on the needle  68  in the clearance regions  74  and/or  70  between the respective top and bottom surfaces of the damper  140  and the corresponding stop surfaces  72  and  77  on armature  46  and needle tip  79 , respectively. For the seat passage  76  opening state, the motion damper  140  abuts against armature  46  and for the seat passage  76  closing state, motion damper  140  abuts against stop surface  77  of needle tip  79 . Thus, the motion damper  140  acts as a counterweight to transfer energy, from the impact of armature  46  and inlet member  24  back to armature  46  for the seat passage  76  opening state, and from the impact of needle  68  and seat  64  back to the needle  68  for the seat passage  76  closing state. The curved surface  78  of needle  68  is preferably a spherical surface that mates with a conical end  80  of a funnel  82  that serves as the preferred seat passage  76  of the seat  64 . During operation, fuel in fluid communication from the fuel inlet source (not shown) flows through the fuel inlet passage  26 , the armature passage  54  of the armature  46 , the body passage  58  of the body  52 , and the seat passage  76  of the seat  64  to be injected from the outlet of the fuel injector  10 . 
     While the present invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims, and equivalents thereof.