Abstract:
An electromagnetically operable fuel injector for a gaseous fuel injection system of an internal combustion engine, the injector having a generally longitudinal axis, 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 being movable away from the fixed valve seat when the magnetic coil is excited. 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 at least a first flow path of gaseous fuel between the armature and the magnetic coil as part of a path leading to the fuel valve. A thermally conductive material is positioned adjacent the magnetic coil to transfer heat from the magnetic coil to adjacent components to as to render the coil thermally efficient and relatively unaffected by heat generated thereby.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present application relates to a thermally efficient compressed natural gas injector having improved performance. 
     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 continuation problems using CNG the fuel injectors inherently present additional problems. For example, problems inherent to generation of heat in the solenoid coil are particularly aggravated in fuel injectors using CNG as will be explained hereinbelow. 
     The CNG (Compressed Natural Gas) injector is required to open and close very quickly to promote efficient fuel consumption. In order to accomplish this objective effectively the magnetic circuit utilized to open the value needle must produce a magnetic field—or flux—relatively quickly across the working gap between the fuel inlet connector and the armature. The CNG injector has a magnetic circuit consisting of an inlet connector, armature, valve body shell, housing and a coil. When energized, the coil produces a magnetic field which is conducted through the magnetic circuit. The flux is conducted through the components and creates an attractive force at the working gap, which force causes upward movement of the armature, with consequent upward movement of the valve needle to open the injector valve. 
     The CNG injector is required to open and close very quickly. This quick opening creates a relatively severe impact between the armature and the inlet connector. In the CNG injector, the factors which effect impact velocity between the armature and inlet connector are more severe then in a gasoline injector. Compared to a gasoline injector, the CNG injector has two to three times the lift, less spring preload and similar force required to open the injector. The difference is then exaggerated by the lower velocity (CNG) fluid then gasoline. 
     A CNG injector requires a much higher flow rate and area to obtain the same amount of energy flow through the injector in a given pulse. This is caused by the lower density of the gaseous CNG when compared to standard gasoline. This requires that the lift for a CNG injector be much greater than it is for a gasoline injector. 
     The increased lift creates several 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. This reduction in force requires the use of a lighter spring preload than in a standard gasoline injector. 
     In addition, with CNG, greater volumes of fuel are made to pass through the injector with increased demands on the solenoid coil and with of excessive heat which adversely affects the temperature and performance of the solenoid. Also, gaseous fuels have a lower specific heat than liquid fuels and thereby tend to conduct less heat away from the solenoid coil. We have invented a fuel injector suitable for use with compressed natural gas which conducts heat from the magnetic solenoid coil to the adjacent components so as to improve performance. 
     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, and a magnetic coil at least partially surrounding the ferromagnetic core. An armature is magnetically coupled to the magnetic coil and is 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 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 is 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. A thermally conductive material is positioned adjacent the magnetic coil to transfer heat from the magnetic coil to adjacent components. Preferably, the thermally conductive material is a thermally conductive plastic material such as nylon. The nylon is filled with reinforcing glass fibers. The glass fiber reinforced nylon is essentially in the form of a cylindrical sleeve about one millimeter (1 mm) in wall thickness and about 5-6 millimeter (mm) in length. 
    
    
     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 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 the improved heat conducting sleeve which surrounds the lower portion of the fuel inlet connector in the area adjacent to the magnetic coil; 
     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; 
     FIG. 4 is a plan view of the bottom surface of the preferred fuel inlet connector shown in FIG. 1; 
     FIG. 5 is an elevational cross-sectional view of a preferred embodiment of the armature shown in FIG.  1  and illustrating the improved fuel flow paths resulting therefrom; and 
     FIG. 6 is an elevational cross-sectional view of the upper portion of a preferred embodiment of the valve body shown in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to FIG. 1 there is shown a CNG injector  10  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. 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 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 . 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 improves 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 features are disclosed in commonly assigned copending applications entitled Compressed Natural Gas Injector with Damping for Armature Needle Assembly during Opening, the disclosure of which is incorporated herein by reference. 
     In addition, as shown in FIG. 4, radial slots in the for 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 0.005 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 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 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 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 damping 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 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, 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 again to FIGS. 1 and 2, Solenoid coil  28  is generally separated from the fuel inlet connectors by a non-magnetic shell  26  which is positioned within the space provided between the solenoid coil  28 , the dielectric material  53 , and the fuel inlet connector  18 . However, prior to the present invention the space immediately above the non-magnetic shell  26  was devoid of any filler material. 
     Since the volume of compressed natural gas passing through a fuel injector is significantly greater than the equivalent volume of liquid fuels (for an equivalent amount of energy) passing through liquid fuel injectors, the solenoid coil  28  tends to undergo increased activity with the result that greater amounts of heat are produced in the area surrounding the solenoid. Furthermore, compressed natural gas tends to remove less heat than comparable amounts of liquid fuels due to a lower specific heat factor. 
     According to the present invention, the annular space located between the upper portion of the solenoid coil enclosure and dielectric plastic material  53  and the fuel inlet connector  18  is filled with a thermally conductive material which assists in conducting heat from the solenoid coil  28  to the non-magnetic shell  26  and the fuel inlet connector  18 . Thereafter the heat is carried out of the injector by the compressed natural gas and the surrounding components. The effect of the provision of such heat conducting material between the solenoid coil  28  and the fuel inlet connector  18  is to reduce coil heat and thereby minimize the effects of the coil temperature and to promote increased performance and efficiency. Further, such heat conducting material can be provided in any spaces in the area generally adjacent the solenoid coil. Although any suitable thermally conductive appropriate material may be used, any type of plastic material, preferably nylon material  27  having a 30 percent (%) glass fiber matrix as a reinforcing filler as shown, is incorporated in the space provided. Other suitable reinforcing filler materials are contemplated. Also, other suitable heat conductive materials, including other polyamides may be used. In FIGS. 1 and 2, the plastic sleeve  27  is shown in cross-section, with schematic representation of a glass fiber filler as indicated by the dots in these Figs. 
     Typically, non-magnetic shell  26  is preferably of stainless steel, is about one millimeter (1 mm) in thickness and is about seven millimeters (7 mm) in length. The glass fiber reinforced nylon material  27  (or nylon “sleeve”) is typically cylindrically shaped, is about one millimeter (1 mm) in thickness and about 5-6 millimeters (mm) in length. 
     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.