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 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 a central fuel opening and a generally annular groove adjacent the central fuel opening, 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. A method of directing gaseous fuel through an electromagnetically operable fuel injector for a fuel system of an ? combustion engine is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present application relates to a compressed natural gas injector which incorporates an improved low restriction valve needle seat to control the fuel flow in the needle valve seat area. 
     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 and to control the flow of fuel through the injector. 
     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. Accordingly, utilizing CNG in engines presents problems unique to CNG as well as to the contaminant levels. 
     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 operate on CNG while remaining contaminant tolerant, the guide and impact surfaces for the armature needle assembly require certain specifically unique characteristics. 
     The CNG injector is required to accurately inject metered pulses of fuel over the life of the injector. It is also necessary to be able to calibrate the injector to a specific calibration. Before it is possible to calibrate a CNG injector, the design must have solved many of the specific problems inherent in using CNG, including higher fuel pressures and needle lift when compared to a standard gasoline injector, choked sonic flow, and pressure losses through the injector. For proper calibration of the injector, the two most important parameters which require control are pressure upstream of the choked flow, and orifice size. 
     In addition, to problems of contaminants in gaseous fuels, other problems relating to flow conditions and pressure losses must also be addressed. For example. whereas in a standard gasoline injector orifice size is a parameter that is controlled to extremely tight tolerances, pressure loss is a CNG, or other gaseous fuel, specific problem which must be considered in the overall design when using gaseous fuels in such injectors. Nevertheless, pressure loss is a natural phenomenon which occurs as fluid flows through any system. As the velocity of the fluid is increased and the fluid is forced through tortuous paths the losses can become quite substantial over the length of the path. These losses contribute directly to the loss of overall mass flow available from the injector. Without proper control of the high pressure loss areas in the injector, static flows would be nearly impossible to correlate. 
     The CNG injector generally has sonic flow exiting the injector. This occurs with CNG any time there is a 55% pressure differential across any given point in the system. While sonic choked flow is achieved, the downstream pressure is no longer included in the mass flow function. The only variables which contribute to the theoretical mass flow in a choked flow system are gas constants, upstream pressure, upstream temperature, and flow area. The gas constants for any given fuel passing through the injector from the fuel rail will be constant from injector to injector, and at present the area for the orifice is controlled very closely for gasoline applications. This leaves pressure and temperature as potential variables. The fuel temperature will not vary significantly from injector to injector due to the short time available for heat transfer. However, the pressure above the orifice is affected by all of the losses throughout the injector and may vary between injectors. 
     As the fuel flows from the fuel rail through the injector, each item comprising the flow path contributes to the total loss in pressure. Some of these losses are small and some are quite substantial. In the present CNG injector art, the main fuel path consists of the filter, upper inlet connector, adjusting tube, armature, valve body, lower guide, lower guide/seat masked area, needle/seat interface and lastly, the orifice. 
     The filter, upper inlet connector, adjusting tube, lower guide and valve body account for a very small portion of the overall pressure loss in the injector. The armature has a small intentional loss to allow for faster breakaway and dampening during opening impact of the valve needle. This leaves only the lower guide/seat interface and the needle/seat interface as the main controllable limiting factors for controlling pressure losses. 
     Theoretically, the needle/seat interface can be controlled through seat angle, spherical needle radius and lift. An increase in lift would reduce the magnetic force of the solenoid coil and lengthen the opening time and linearity of the injector. As the spherical radius of the needle increases, it thereby increases the exposed area for a given lift with the result that the net force of the gas pressure increases. This also lengthens the opening time of the injector. Presently such injectors utilize a needle/seat angle of approximately 90°. If the seat angle is increased from the present 90° angle, the flow area exposed for a given lift also increases as long as the needle spherical radius is changed to accommodate the reduced sealing diameter. This concept, although appearing relatively simple, has several serious drawbacks. 
     When the seat angle is increased, two problems occur. The first problem is that the increased seat angle is more difficult to grind on existing seat grinding equipment. A good compromise between grinding capabilities and design can be reached to reduce the effect of this problem. The second problem is that the flow past the lower needle guide/seat interface becomes pinched and the flow loss from this interface becomes significant. The present invention provides significant flow control while avoiding the loss of fuel flow through a novel valve structure which incorporates a novel valve needle seat. 
     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, an armature magnetically coupled to the magnetic coil and being movably responsive to the magnetic coil, the armature actuating a valve closing element which interacts with a fixed valve seat of a fuel valve and being movable away from the fixed valve seat when the magnetic coil is excited. The fixed valve seat of the fuel valve defines a central fuel opening and a generally annular groove adjacent the central fuel opening, 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 the fuel valve. 
     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, an armature magnetically 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 fuel valve having a fixed valve seat to selectively permit fuel to pass through the valve seat as the valve closing element is moved to a valve open position by the armature. The fixed valve seat has a generally frusto-conically shaped portion surrounded by an adjacent circular shaped annular groove to reduce the pressure differential occurring across the valve closing element and the fixed valve seat upon closing the fuel valve. A fuel inlet connector extends in a generally longitudinal direction above the armature and defines a path for fuel to enter the inlet connector and 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, and further defines a generally axial fuel passage. 
     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 is positioned at the fuel inlet end portion and has a fuel inlet end portion and a fuel outlet 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 providing an annular groove adjacent the fixed valve seat for reception of fuel so as to reduce pressure losses across the fuel valve during closure thereof. In particular, the fuel is permitted to enter in volumetric space adjacent the fuel valve to reduce the pressure losses thereacross during closure of the fuel valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described hereinbelow with reference to the drawings wherein: 
     FIG. 1 is an elevational view, partially in cross-section, of a preferred embodiment of a compressed natural gas injector incorporating a valve needle seat constructed according to the invention; 
     FIG. 2 is an enlarged elevational cross-sectional view of the lower portion of the injector of FIG. 1, showing an enlarged view of the valve needle seat shown 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 FIGS. 1 and 2; 
     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 and illustrating the improved fuel flow paths resulting therefrom; 
     FIG. 6 is an elevational cross-sectional view of the upper portion of a preferred embodiment of the valve body shown in FIGS. 1 and 2; 
     FIG. 7 is an enlarged cross-sectional view of a valve needle seat of the type presently used in such injectors, the valve needle being shown in a “valve open” position; and 
     FIG. 8 is an enlarged cross-sectional view of an improved valve needle seat constructed according to the present invention and as shown in the injector in FIGS. 1 and 2, the valve needle being shown in a “valve open” position. 
     FIG. 9 is view taken along lines  9 — 9  of FIG. 2, illustrating a preferred valve needle lower guide having arcuately shaped fuel passage openings. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to FIG. 1 there is shown a CNG injector which is constructed according to the present invention. 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 are 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, and U.S. application Ser. No. 09/320,176, filed May 26, 1999, entitled Compressed Natural Gas Injector Having Improved Low Noise Valve Needle, 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, U.S. application Ser. No. 09/320,175, filed May 26, 1999, entitled Gaseous Injector with Columnated Jet Orifice Flow Directing Device and U.S. application Ser. No. 09/320,179, filed May 26, 1999, entitled Compressed Natural Gas Injector Having Magnetic Pole Face Flux Director, 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). 
     Referring further to FIG. 1 in conjunction with FIG. 2, valve body shell  32 , which is made of a ferromagnetic material and which forms part of a magnetic circuit, surrounds valve body  34  and 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 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 frusto-conical cross-sectional shape. 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 . 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 . Armature upward and downward movement is permitted by interface space  15  (or working gap) between the inlet connector  18  and the armature  14 . The working gap is generally extremely small i.e. in the order of about 0.3 mm (millimeters). Solenoid coil  28  is surrounded by dielectric plastic material  53  as shown in the 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 with conventional fuels which are relatively free of contaminants such as water, solids, oil, 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. 
     When known injectors, which functioned at relatively acceptable levels with relatively clean conventional fuels, were utilized with CNG, 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. 
     The present injector eliminates the aforementioned erratic valve closing and improve the operation of the injector with gaseous fuels. 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. 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. Additional related features are also disclosed in the aforementioned commonly assigned copending application entitled Compressed Natural Gas Injector Having Gaseous Dampening For Armature Needle Assembly During Opening. 
     In addition, as shown in FIG. 4, radial slots in the form 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 0.005 mm in height, thus creating six corresponding 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 valve, 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 collection of solid contaminants which are ultimately removed by the flow of 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, provide a unique fuel flow path past 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 the 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 still another significant improvement which renders the present 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 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  in the armature as shown in FIG. 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 armature  14  in FIG.  1 . The fuel flowing through aperture  60  is indicated 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 . When the needle  16  is lifted, the fuel is permitted to enter aperture  41  and 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 inlet connector lowermost face—create a fuel flow pattern which induces the CNG to flow in the manner shown by the fuel flow lines at  56   61  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 and inlet connector 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 provision of radial pads on the face of the inlet connector, and the unique CNG flow patter 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, as noted, 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 application 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 FIGS. 7 and 8 there is shown a comparison between the valve needle seat of the type used in earlier developments, and the low restriction valve needle seat constructed according to the present invention. 
     In FIG. 7, there is illustrated a tip portion  17  of a valve needle  16  of the type shown in FIGS. 1 and 2, in combination with a valve needle seat  82  of the type used in earlier developments. Lower needle guide  80  is shown in cross-section in combination with the tip portion  17  of needle  16 , and is also shown in FIG.  9 . As can be seen, the valve needle seat  82  has a frusto-conically shaped needle rest, all sides of which form an angle of approximately 90°, and a valve orifice  81  which, together with the needle rest surfaces  84 ,  86  form a funnel like arrangement through which the gaseous fuel must pass. Although needle rest surfaces  85 ,  86  actually form part of the same frust-conical surface, they are referred to separately for convenience of the description. 
     In contrast to the valve needle seat shown in FIG. 7, the valve needle seat  40  constructed according to the present invention is shown in FIG.  8 . Referring to FIG. 8, it can be seen that the valve needle seat  40  includes frusto-conical valve needle seat surface  88 , which is continuous and which forms an angle of approximately 90° in cross-section. However, valve needle seat  40  also includes an arcuate circular annular groove  92  having an arcuate surface  94  as shown, which connects the vertical surface and the horizontal surface of the groove  92  as shown. The function and purpose of groove  92  will best be appreciated by referring to FIG. 9, which illustrates a plan view of lower valve needle guide  80 . 
     Referring now to FIG. 9, lower valve needle guide  80  includes arcuate apertures  96  which permit the flow of gaseous fuel therethrough for passage through valve aperture  41 . Although arcuate apertures  96  are relatively large, the lower valve needle guide nevertheless tends to present a restriction to the passage of gaseous fuel thereby. Accordingly, in the structure shown in FIG. 7, as the needle  16  moves downwardly toward the valve seat  82  to pinch the flow at the contact points  43 , immediately prior to actual contact, the pressure differential across the contact points  43  is substantial in that the pressure between the lower valve guide and the contact points  43  is substantially greater than the pressure on the opposite side of the contact points  43  just prior to contact being completed. In fact, the presence of the lower needle guide  80  tends to increase the pressure in the zone immediately above the contact points  43 . Although “contact points  43 ” are referred to as “points,” they each in fact are points on the same circle formed by the points of tangency between the arcuate needle contact surface and the needle rest surface. However, they are referred to separately for convenience of the description. 
     In contrast thereto, as shown in FIG. 8, the presence of the annular groove  92  which is provided in the needle valve seat tends to reduce the differential pressure across the seal points  43  by providing additional volumetric space between the lower needle guide  80  and the valve seat  40 . Thus, the pressure differential across the seal points  43  is somewhat reduced thereby reducing the flow reducing pressure losses otherwise occurring across the point of contact between the needle  16  and the valve seat  40 . Since such pressure losses tend to reduce the fuel flow passing through the injector, the provision of the unique valve seat  40  as shown in FIG. 8 has been found to avoid such reduction in fuel flow which occurs normally as a result of such pressure losses. This factor increases the energy flow into the engine with correspondingly increased efficiency. 
     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.