Abstract:
An electromagnetically operable fuel injector for a gaseous fuel injection system of an internal combustion engine, the injector having a generally longitudinal axis, which includes a ferromagnetic core, a magnetic coil at least partially surrounding the ferromagnetic core and an armature magnetically coupled to the magnetic coil and being movably responsive to the magnetic coil. The armature actuates a valve closing element in the form of a valve needle which interacts with a fixed valve seat of a fuel valve and is movable away from the fixed valve seat when the magnetic coil is excited. The fixed valve seat defines an aperture of predetermined dimension for passage of fuel therethrough, the armature having a generally elongated shape and a generally central opening for axial reception and passage of gaseous fuel from a fuel inlet connector positioned adjacent thereto. The fuel inlet connector and the armature are adapted to permit a first flow path of gaseous fuel between the armature and the magnetic coil as part of a path leading to said fuel valve. An orifice device is positioned downstream of the fuel valve and defines an orifice for reception of fuel from the fuel valve, the orifice being of lesser dimension than the aperture of said fixed valve seat. A method of directing gaseous fuel through an electromagnetically openable fuel injector in a manner which provides dampening of the valve needle upon closing is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present application relates to a compressed natural gas injector which provides armature needle dampening during closing of the fuel valve. 
     2. Description of the Related Art 
     Compressed natural gas (hereinafter sometimes referred to as “CNG”) is becoming a common automotive fuel for commercial fleet vehicles and residential customers. In vehicles, the CNG is delivered to the engine in precise amounts through gas injectors, hereinafter referred to as “CNG injectors”. The CNG injector is required to deliver a precise amount of fuel per injection pulse and maintain this accuracy over the life of the injector. In order to maintain this level of performance for a CNG injector, certain strategies are required to help reduce the effects of contaminants in the fuel. 
     Compressed natural gas is delivered throughout the country in a pipeline system and is mainly used for commercial and residential heating. While the heating systems can tolerate varying levels of quality and contaminants in the CNG, the tolerance levels in automotive gas injectors is significantly lower. 
     These contaminants, which have been acceptable for many years in CNG used for heating, affect the performance of the injectors to varying levels and will need to be considered in future CNG injector designs. Some of the contaminants found in CNG are small solid particles, water, and compressor oil. Each of these contaminants needs to be addressed in the injector design for the performance to be maintained over the life of the injector. 
     The contaminants can enter the pipeline from several sources. Repair, maintenance and new construction to the pipeline system can introduce many foreign particles into the fuel. Water, dust, humidity and dirt can be introduced in small quantities with ease during any of these operations. Oxides of many of the metal types found in the pipeline can also be introduced into the system. In addition, faulty compressors can introduce vaporized compressor oils which blow by the seals of the compressor and enter into the gas. Even refueling can force contaminants on either of the refueling fittings into the storage cylinder. Many of these contaminants are likely to reach vital fuel system components and alter the performance characteristics over the life of the vehicle. 
     In general, fuel injectors require extremely tight tolerances on many of the internal components to accurately meter the fuel. For CNG injectors to remain contaminant tolerant, the guide and impact surfaces for the armature needle assembly require certain specifically unique characteristics. 
     In addition to fuel contamination problems using CNG, the fuel injectors inherently present additional problems. For example, the problems inherent to dampening or lack of dampening of the needle/armature assembly upon closing as well as upon opening of the fuel valve are unique to fuel injectors utilizing CNG. 
     The CNG injector is required to open and close very quickly. This quick closing creates a relatively severe impact between the armature and the seat. In the CNG injector, the factors which affect impact velocity between the armature and inlet connector are more severe than in a gasoline injector. The CNG injector has high lift, and lower viscosity (CNG) fluid when compared with a gasoline injector. 
     A CNG injector requires much higher flow area to get the same amount of energy flow through the injector during a given pulse. This is caused by the lower density of the gaseous CNG when compared to standard liquid fuels such as gasoline. This requires that the lift for a CNG injector valve needle be greater than that of a standard gasoline injector. 
     The increased lift creates two problems. First, the increased lift increases the amount of energy stored in the spring. This high potential energy stored in the spring is required to allow the injector to operate consistently as the viscosity of the fuel changes. Second, the velocity reached during the longer flight times can be high, creating higher impact forces. We have invented a fuel injector which incorporates a flow restricting orifice device which assists in dampening of the armature/needle assembly upon closing in a manner which improves performance of the engine, particularly when utilized in a fuel injector having several fuel flow paths therethrough, a feature which avoids the problems inherent with contaminated compressed natural gaseous fuels. 
     SUMMARY OF THE INVENTION 
     An electromagnetically operable fuel injector for a gaseous fuel injection system of an internal combustion engine is disclosed, the injector having a generally longitudinal axis, which comprises a ferromagnetic core, a magnetic coil at least partially surrounding the ferromagnetic core, and an armature magnetically coupled to the magnetic coil and being movably responsive to the magnetic coil. The armature actuates a valve closing element which interacts with a fixed valve seat of a fuel valve and is movable away from the fixed valve seat when the magnetic coil is excited. The fixed valve seat defines an aperture of predetermined dimension for passage of fuel therethrough. The armature has a generally elongated shape and a generally central opening for axial reception and passage of gaseous fuel from a fuel inlet connector positioned adjacent thereto. The fuel inlet connector and the armature are adapted to permit a first flow path of gaseous fuel between the armature and the magnetic coil as part of a path leading to the fuel valve. An orifice device is positioned downstream of the fuel valve and defines an orifice for reception of fuel from the fuel valve, the orifice being of lesser dimension than the aperture of the fixed valve seat. 
     In a preferred embodiment, an electromagnetically operable fuel injector for a compressed natural gas fuel injection system of an internal combustion engine is disclosed, the injector having a generally longitudinal axis, which comprises a ferromagnetic core, a magnetic coil at least partially surrounding the ferromagnetic core, and an armature coupled to the magnetic coil and movably responsive to the magnetic coil, the armature having a first upper end face and a lower end portion. A valve closing element is connected to the lower end portion of the armature and is interactive with a fixed valve seat which defines a fuel passage aperture to selectively permit fuel to pass through the aperture as the valve closing element is moved to a valve open position by the armature. An orifice device is positioned adjacent and downstream of the fuel valve, the orifice device having an orifice in general alignment with the fuel passage aperture and being dimensioned less than the aperture to restrict the flow of fuel from the fuel valve to thereby provide dampening of the valve closing element upon closing. A fuel inlet connector extends in a generally longitudinal direction above the armature and defines a path for fuel to enter the fuel inlet connector to be directed toward the armature, the fuel inlet connector having a lowermost end portion having a lowermost surface spaced above the armature to define a working gap through which the armature is movable. The armature has a fuel reception portion for receiving fuel directed from the fuel inlet connector. The armature further defines a generally axial fuel passage and at least a first fuel flow aperture extending through a wall portion thereof for directing fuel from the fuel inlet connector through the generally axial fuel passage and into the aperture toward the fixed valve seat for entry into an air intake manifold for the engine. The fuel flow aperture is oriented generally transverse to the longitudinal axis. 
     A method of directing gaseous fuel through an electromagnetically operable fuel injector for a fuel system of an internal combustion engine is also disclosed, the injector having a generally longitudinal axis, and including a fuel inlet end portion and a fuel outlet end portion, a fuel inlet connector positioned at the fuel inlet end portion and having a fuel inlet end portion. An armature is positioned adjacent the fuel outlet end portion of the fuel inlet connector, the armature being spaced from the fuel inlet connector to define a working gap to permit movement of the armature toward and away from the fuel inlet connector to selectively open and close a fuel valve by providing upward and downward movement of a valve closing element to selectively permit gaseous fuel to pass therethrough to an air intake manifold. The method comprises directing the gaseous fuel to pass axially through the fuel inlet connector, directing the gaseous fuel to pass from the fuel inlet connector to the generally elongated central opening of the armature in an axial direction toward the fuel valve, and restricting the passage of fuel exiting from the fuel valve so as to provide dampening of the valve closing element upon closing of the fuel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described herein below with reference to the drawings wherein: 
     FIG. 1 is an elevational view, partially in cross-section, of a compressed natural gas injector of the type contemplated herein; 
     FIG. 2 is an enlarged elevational cross-sectional view of the lower portion of the injector of FIG. 1, modified to incorporate a flow restricting orifice device downstream of the fuel valve according to the present invention, other features being the same as in FIG. 1; 
     FIG. 3 is a partial elevational cross-sectional view of the lower end portion of the fuel inlet connector of the injector shown in FIG. 1, incorporating features to assist the injector in utilizing CNG; 
     FIG. 4 is a plan view of the bottom surface of the preferred fuel inlet connector shown in FIGS. 1 and 2; 
     FIG. 5 is an elevational cross-sectional view of a preferred embodiment of the armature shown in FIGS. 1 and 2, illustrating fuel flow paths resulting therefrom; 
     FIG. 6 is an elevational cross-sectional view of the upper portion of the valve body shown in FIGS. 1 and 2; 
     FIG. 7 is a view taken along lines  7 — 7  of FIG. 2, illustrating the lower valve needle guide; 
     FIG. 8 is a cross-sectional view of the valve needle seat shown in FIG. 2, illustrating the flow restricting orifice according to the present invention, with the tip of the valve needle in the “valve open” position; 
     FIG. 9 is a cross-sectional view similar to FIG. 8, with the tip of the valve needle in the “nearly closed” position; and 
     FIG. 10 is a cross-sectional view similar to FIG. 9, with the tip of the valve needle in the “valve closed” position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to FIG. 1 there is shown a CNG injector  10  of the type contemplated herein for incorporation of a flow restricting orifice device according to the present invention as will be shown and described particularly in connection with FIG.  2 . Injectors of the type contemplated herein are described in commonly assigned U.S. Pat. No. 5,494,224, the disclosure of which is incorporated by reference herein. Injectors of this type as also disclosed in commonly assigned copending applications; U.S. application Ser. No. 09/320,178, filed May 26, 1999, entitled Contaminant Tolerant Compressed Natural Gas Injector and Method of Directing Gaseous Fuel Therethrough, pending, and U.S. application Ser. No. 09/320,176, filed May 26, 1999, entitled Compressed Natural Gas Injector Having Improved Low Noise Valve Needle, pending, the disclosures of which are incorporated herein by reference. Other commonly assigned, copending applications include U.S. application Ser. No. 09/320,177, filed May 26, 1999, entitled Compressed Natural Gas Injector with Gaseous Damping for Armature Needle Assembly During Opening, now allowed, U.S. application Ser. No. 09/320,175, field May 26, 1999, entitled Gaseous Injector with Columnated Jet Orifice Flow Directing Device, now allowed, and U.S. application Ser. No. 09/320,179, filed May 26, 1999, entitled Compressed Natural Gas Injector Having Magnetic Pole Face Flux Director, pending, the disclosures of which are also incorporated herein by reference. 
     The injector  10  includes housing  12  containing armature  14  to which valve needle  16  is attached by crimping in a known manner. Fuel inlet connector  18  includes central fuel flow opening  13  and CNG filter  20  at the upper end portion of opening  13  as shown. The fuel inlet connector  18  also includes adjusting tube  22  connected thereto at  24  by a known crimping procedure. Housing  12  includes inner non-magnetic shell  26  which surrounds the inlet connector  18  and armature  14  having central fuel flow opening  11  as shown. Armature  14  and fuel inlet connector  18  define with housing  12 , an enclosure for solenoid coil  28  which is selectively energized to move armature  14  and needle  16  upwardly to open the valve aperture  41 , and selectively deenergized to permit armature  14  and needle  16  to return to the “closed valve” position as shown, under the force of coil spring  30 . Fuel flow into the injector begins at filter  20  and passes through fuel inlet connector  18 , to armature  14 , and ultimately to valve aperture  41  of valve seat  40  into the intake manifold of the engine (not shown). Valve seat  40  shown in FIG. 1 is a type which does not incorporate the flow restricting orifice device of the present invention. However in the fuel injector of the present invention as shown in FIG. 2, the remaining structural features shown in FIG. 1 are the same. 
     FIG. 2 illustrates an injector similar to the injector shown in FIG. 1, modified to include the flow restricting orifice device  82  downstream of the fuel valve  40  as shown, and retained by crimped retaining washer  83 . Referring further to FIG. 2 in conjunction with FIG. 1, valve body shell  32 , which is made of a ferromagnetic material and which forms part of a magnetic circuit, surrounds valve body  34  that has at the upper end, upper guide  36  as shown. Space  36   a  between upper guide  36  and armature  14  is about 0.010 to about 0.015 mm on the diameter, and permits guiding movement of armature  14 . Lower O-rings  38  provide sealing between the injector  10  and the engine intake manifold (not shown) and upper O-rings  39  provide sealing between the injector  10  and the fuel rail (also not shown). Valve body  34  defines central fuel flow opening  35 . 
     In FIG. 2, valve body shell  32  is attached to valve body  34 , preferably by weld  32   a , and at the upper end by weld  26   a , to non-magnetic shell  26 . Non-magnetic shell  26  is in turn welded to fuel inlet connector  18  at  26   b . Thus, fuel flowing from fuel inlet connector  18  across working gap  15  must flow through the clearance space  14   a  between armature  14  and valve body shell  32  which is also provided to permit upward and downward movement of armature  14 . The space  14   a  is approximately 0.10 to 0.30 mm on the diameter. 
     Referring again to FIGS. 1 and 2, valve seat  40  contains a valve orifice  41  and a funnel shaped needle rest  42  having a generally frusto-conical cross-sectional shape. In FIG. 1 the valve seat  40  is maintained in position by back-up washer  44  and sealed against fuel leakage with valve body  34  by O-ring  46 . 
     The valve seat  40  constructed according to the invention is shown in FIG. 2, and includes flow restricting orifice device  82  which has orifice  84  of lesser diameter than valve aperture  41 . Orifice device  82  is held in position by crimped back-up washer  83  as shown. Thus, orifice device  82  serves to restrict the gaseous fuel flow passing through fuel valve  40  to increase the fuel pressure between the tip  17  of needle  16  and orifice device  84  so as to dampen the downward movement of needle  16  during the “valve closing” portion of the armature/needle movement cycle. In general, aperture  41  of fuel valve  40  is circular and is in the range of about 1.9 to about 2.2 mm (millimeters), and orifice  84  of orifice device  82  is circular and is in the range of about 1 mm to about 1.8 mm (millimeters). Accordingly, the range of possible ratios of valve aperture  41  size to orifice size is in the range of about 1.06 to about 2.2. 
     Overmold  48  of suitable plastic material such as nylon supports terminal  50  which extends into coil  28  and is connected via connection  51  to provide selective energization of the coil to open the valve by raising the armature  14  and valve needle  16  against the force of spring  30 . Solenoid coil  28  is surrounded by dielectric plastic material  53  as shown in FIGS. 
     In injectors of this type, the interface space  15  (or working gap  15 ) between the inlet connector and the armature is extremely small, i.e. in the order of about 0.3 mm (millimeters), and functions relatively satisfactorily to permit armature upward and downward movement with conventional fuels which are relatively free of contaminants such as water, solids, oils, or the like, particularly after passing through a suitable fuel filter. Accordingly, when the two surfaces surrounding space  15  are in such intimate contact that the atmosphere between them is actually displaced in relatively significant amounts, atmospheric pressures acting on the two members actually force the two surfaces together. Any liquid contaminant present at the armature/inlet connector interface would allow for the atmosphere to be displaced, thereby adversely affecting the full and free operation of the armature/needle combination. 
     As noted previously, the utilization of CNG with fuel injectors presents several problems certain of which are related to contaminants in the fuel and others of which are related to the flow characteristics of gaseous fuels as compared to liquid fuels. When known injectors, which functioned at relatively acceptable levels with relatively clean conventional fuels, are utilized with CNG without inventive structural modifications, impurities such as oil or water at the inlet connector/armature interface produced a force of about 16.5 Newtons holding the armature to the inlet connector. In comparison, the force provided by spring  30  is in the order of about 3 Newtons, thus fully explaining the erratic closing of the armature/valve needle when the fuel utilized with known injectors is CNG. In particular, the 16.5 Newton force holding the inlet connector and armature together is due to the fact that the fuel operating pressure within the injector is about 8 bar (i.e. 8 atmospheres) and this force of about 16.5 Newtons acts across the lower surface area of the inlet connector  18 , which is about 21 square millimeters (i.e. mm 2 ). Thus a relatively minor slick of oil or other impurity within space  15  of a known injector will cause the inlet connector and the armature to become temporarily attached to each other, particularly due to the 8 bar pressure acting on the remaining surfaces of the inlet connector and armature. As noted, the tendency for the armature to become attached to the inlet connector results in erratic valve closing. 
     Significant features of the present injector are provided inter alia, contribute toward elimination of the aforementioned erratic valve closing and improve the operation of the injector. In FIG. 3, the lower end portion of inlet connector  18  is configured as shown, by the arcuately chamfered end  52 . This configuration provides a beneficial effect in that it directs and orients the magnetic field across the working gap  15  in a manner which optimizes the useful magnetic force created for moving the armature through the working gap  15  in a manner which optimizes the useful magnetic force created for moving the armature through the working gap. This feature is disclosed in commonly assigned application entitled Compressed Natural Gas Fuel Injector Having Magnetic Pole Face Flux Director, the disclosure of which is incorporated herein by reference. 
     In addition, as shown in FIG. 4, radial slots in the form of recessed surfaces  18   a  are provided in the lowermost surface of inlet connector  18  to reduce the effective contact surface area between the armature and the inlet connector by about one third of the total cross-sectional area which was utilized in prior art conventional injectors. This configuration provides six coined pads  18   b  of about 0.05 mm in height, thus providing six corresponding generally rectangular shaped radial slots  18   a  to provide fuel flow paths. By reducing, the effective surface area of the lowermost face of the inlet connector  18  as shown, the tendency to develop an attractive force between the inlet connector  18  and the armature  14 , is significantly reduced to about one-third of its original value, and the ability to tolerate fuel contaminants at the interface without producing an attractive force therebetween is also significantly increased. As noted, preferably, the rectangular radial slots  18   a  are of a shallow depth, i.e. about 0.05 mm, (i.e., millimeters) in order to provide the benefit of reducing the inlet connector/armature interface surface area while still providing a relatively unobtrusive location for temporary collection of solid contaminants which are ultimately removed by the flow for gaseous CNG. 
     As noted, the provision of recessed surfaces  18   a  in the lowermost surface of inlet connector  18  creates raised pads  18   b  on the surface, which pads improve the tolerance of the injector to fuel contaminants in several ways. The recessed surfaces  18   a  may be made by any suitable process, but are preferably coined. The first effect is to reduce the contact area of the inlet connector at the armature interface, thereby significantly reducing any attractive force generated therebetween by liquid contaminants such as oil or water. Furthermore, as noted, the radial pads  18   b  provide hidden areas between the pads where contaminants can collect without affecting the operative working gap  15  until being drawn away by the fuel flow. The working gap for gasoline is about 0.08 mm to about 0.14 mm and about 0.3 mm for compressed natural gas. In addition, as noted, the provision of the six rectangular recessed portions in the form of slots  18   a  and six raised pads  18   b , each having a generally trapezoidal shape, on the inlet connector, provides a unique fuel flow path past the inlet connector/armature interface in a manner which causes the gaseous fuel to pass transversely through the working gap  15  as shown at  56  in FIG.  5  and allow for the control of the fuel flow around and through the armature by controlling the pressure losses. 
     Also by controlling the sizes of the recessed surfaces  18   a  and raised pads  18   b , and the various apertures  58 ,  60 ,  66  in the armature and the valve body as will be described—as well as the numbers and combinations of such openings—the fuel flow can be controlled over at least three flow paths and pressure losses can also be controlled. For example, a small pressure differential across the armature while fully open, assists spring  30  during breakaway upon closing and provides dampening on opening impact. The additional fuel flow path also reduces the possibility of contaminants collecting above upper guide  36  as shown in FIG.  2 . In summary, numerous combinations of apertures and sizes thereof—as well as slots and pads on the fuel inlet connector—can be made to direct the gaseous fuel flow in any desired manner which is best for optimum fuel burning and engine application. 
     Referring now to FIGS. 5 and 6 in conjunction with FIGS. 1-3, there is illustrated a feature which renders the fuel injector assembly more fully capable of operation with CNG. In injectors which were used with relatively contaminant free liquid fuels the fuel would pass through the filter and down through the inlet connector into the armature and out an opening positioned relatively close to the lowest portion of the armature which was located substantially immediately above the valve aperture. In the present structure there is provided a relatively diagonally oriented aperture  58  shown in FIGS. 2 and 5, which directs the CNG flow therethrough and downwardly toward valve aperture  41  for entry into the intake manifold of the internal combustion engine. 
     As shown in FIG. 5, aperture  58  forms a generally acute angle with longitudinal axis A—A of the fuel injector  10 . In addition, the armature of the present invention provides at least one side opening  60  which is generally transverse to the longitudinal axis A—A, to permit fuel flowing downwardly through the center of the armature to be directed sidewardly out of the armature and thereafter downwardly toward the valve aperture  41  shown in FIG.  1 . In the embodiment shown in FIG. 1, aperture  60  is generally horizontal, but may be oriented at an acute angle to the longitudinal axis if desired. Aperture  58  is not shown in the cross-sectional view of FIG.  1 . The fuel flowing through aperture  60  is indicated in FIG. 5 by the flow lines  62  and the fuel flowing through aperture  58  is indicated schematically by flow lines  64 . Optionally several additional horizontal apertures  60  may be provided in the armature at different radial locations thereabout, or alternatively as shown, one aperture  60  may be provided, depending upon the fuel flow pattern sought in each particular instance. It can be seen that the fuel flow from the fuel inlet connector  18  is divided into three paths, a first path expanding across working gap  15 , a second path through aperture(s)  60 , and a third path through aperture(s)  58 . The first path extends between the armature  14  and the magnetic coil  28  and is ultimately joined by the second flow path passing through aperture(s)  60 . 
     It can also be readily appreciated that the diameters of each aperture  58 ,  60  can be varied to direct the fuel flow in any predetermined desired direction. For example, by reducing the size of apertures  58 ,  60  fuel will be encouraged to flow with increased volume cross the working gap  15 . Alternatively, increasing the diameter of apertures  58 ,  60  will attract greater volume of fuel through those apertures and thereby reduce the fuel flow across the working gap. It has also been found that the diameters of the apertures  58 ,  60  and the numbers and locations of such apertures affect the dampening characteristics of the valve needle  16 , both upon opening and upon closing. Accordingly, the diameter of fuel flow apertures  58 ,  60  and the numbers, locations, and orientations of such apertures will depend upon the desired volumetric flow characteristics and desired flow patterns in each instance; however diameters within the range of 1-2 mm have been found to be preferable. 
     Referring now to FIG. 6, a valve body  34  is also provided with central fuel flow opening  35  and several diagonally oriented fuel path apertures  66  which are intended to receive the CNG fuel flowing from the first and second flow paths from the working gap  15  and aperture(s)  60  along the sides of the armature  14  and to redirect the fuel downwardly toward the valve aperture  41 . Thus, when the needle  16  is lifted, the fuel is permitted to enter aperture  41  and is thereafter directed into the intake manifold of the engine, which is not shown in the drawings. Fuel flowing along the third flow path through aperture(s)  58  lead directly toward aperture  41 . It has been found that the unique provisions of the apertures  58  and  60 —as well as rectangular radial slots  18   a  on the lowermost face of the inlet connector—create a fuel flow pattern which induces the CNG to flow in the manner shown by the fuel flow lines at  56 ,  62  and  64  in FIG. 5, and such fuel flow lines actually create ideal pressure conditions to avoid causing the armature to be attracted to the inlet connector. Thus the attractive forces between the armature  14  and inlet connector  18  are minimized by the several factors mentioned, namely the elimination of the tendency of the oil and contaminates to accumulate in the space  15  located between the armature and the inlet connector, the reduction of the effective inlet connector/armature interface area by the provision of radial pads on the face of the inlet connector, and the provision of the unique CNG flow pattern which creates a force free environment between the inlet connector and the armature. 
     As indicated, alternatively, apertures  60  may be provided in several locations about the circumference of the armature, and apertures  58  may be provided in several locations thereabout. Also their angular orientations may be varied. However, it has been found that a single aperture on each side, as shown, is sufficient to produce the desired flow path and the force free environment. Also, it should be noted that the diameter of each aperture can be altered in order to provide control of the fuel pressures and flow patterns in the areas surrounding the inlet connector, the armature, and the valve body, so as to provide a predetermined fuel flow pattern throughout the injector as may be desired. This feature is more fully disclosed in the aforementioned commonly assigned, copending applications entitled Compressed Natural Gas Injector Having Gaseous Damping for Armature Needle Assembly During Opening. 
     It should also be noted that the presence of the diagonally oriented fuel flow apertures  66  in valve body  34  eliminates the problems of prior art injectors wherein debris and contaminants would accumulate in the area of the upper valve guide  36 , causing abrasive action and intermittent guidance between the upper guide  36  and the armature  14 . Thus, the provision of the diagonally oriented apertures  66  in valve body  34  encourage the flow of CNG past the area surrounding the upper guide  36  and eliminate any accumulation tendencies for contaminants in the area of upper guide  36 . 
     Referring now to FIG. 7, in conjunction with FIG. 2, lower valve needle guide  80  is illustrated in the form of a disc shaped member having arcuately shaped fuel passage apertures  90  which direct the gaseous CNG toward valve aperture  41 . 
     The stages through which a CNG injector undergoes while closing begin with de-energizing of the solenoid coil and decay of the magnetic flux. Next, the magnetic force decays to a level less than the combined spring and gas force acting on the needle armature assembly, causing the needle armature to move toward the seat. As the valve needle approaches the valve seat, the gas flowing out of the injector is sealed at the needle seat interface and the injector valve closes. These three phases are characterized at the needle seat interface in the stages of closing which are illustrated in FIGS. 8,  9  and  10 , respectively. In particular, FIG. 8 shows tip  17  of needle  16  in the open position, FIG. 9 shows needle tip  17  in the nearly closed position, and FIG. 10 shows needle tip  17  in the fully closed position. 
     To exit the injector  10  the fuel passes through apertures  90  in the lower guide  80 , and thereafter between the needle tip  17  and seat interface. The fuel then passes through the seat aperture  41  and exits through the orifice. When the injector is fully open, the CNG injector has sonic choked flow at the orifice  84 . Choked flow will occur whenever the pressure drop is greater than 55% across any point in the system. In the present instance, the flow is choked at the orifice  84  of orifice device  82  while the injector needle  16  is fully open. Also, the flow is choked at the needle seat when the needle  16  is nearly closed. 
     When the CNG injector is fully closed as shown in FIG. 10, the needle return coil spring  30  accounts for about ¼ of the total force on the needle armature assembly. The other ¾ force is made up of the compressed gas forcing the needle into the seat caused by the differential pressure between the internal injector and the pressure in the intake manifold of the engine. To dampen the needle armature assembly during closing, the downward force on the needle  16  caused by the differential gas pressure is delayed by the presence of orifice device  82  for a short period of time when the injector is nearly closed. 
     As the needle approaches the valve seat  40  under the force of the coil spring  30 , the sonic flow condition transfers from the orifice  84  to the needle seat interface. By controlling the duration of this transfer time the level of dampening can be varied. In particular, the time to transfer the sonic flow from the orifice to the needle/seat interface is controlled by the volume between the needle/seat interface and the orifice  84 . The diameter of the orifice  84  also affects the transfer of the sonic flow condition. When the injector is open, fully established flow is choked at the orifice. Before the transfer of the choked flow from the orifice to the needle/seat interface can take place, a 55% pressure drop must occur at the needle/seat interface. In particular, the pressure must decay in the region between the needle/seat interface and the orifice  84 . Before the pressure in this region decays, the coil spring  30  has the most influence on the velocity of the needle/armature assembly. Once the flow is choked at the needle/seat interface, the additional force to close the injector valve is provided by the differential gas pressure acting on the needle  16 . 
     Although the invention has been described in detail with reference to the illustrated preferred embodiments, variations and modifications may be provided within the scope and spirit of the invention as described and as defined by the following claims.