Patent Publication Number: US-6341597-B1

Title: Fuel injection system for high vapor pressure liquid fuel

Description:
RELATED APPLICATIONS 
     This application claims the benefit of priority of provisional patent application Ser. No. 60/106,765 filed Nov. 3, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates in general to fuel injection systems and in particular to fuel injection systems for handling high vapor pressure liquid fuel. 
     A problem with high pressure fuel injection systems is supplying each fuel injection valve with enough liquid fuel to insure reliable engine starting. One aspect of the problem is the presence of vapor bubbles in the injectors. The vapor bubbles must be flushed out and replaced with liquid fuel for reliable engine starting. The problem is more severe in a hot-start condition wherein fuel is present in vapor form in the fuel lines and in the individual fuel injection valves. The vapor bubbles must be rapidly flushed out from the injectors and the injectors cooled down. 
     SUMMARY OF THE INVENTION 
     The present invention provides a fuel injection system comprising at least two fuel injectors; each fuel injector including at least one fuel inlet and at least one vapor outlet, the at least one vapor outlet being located vertically higher than the at least one fuel inlet; at least two pods, one fuel injector being inserted in each pod, respectively; each pod including a fuel inlet connection in fluid communication with the at least one fuel inlet of the injector and a fuel return connection in fluid communication with the at least one vapor outlet of the injector, the fuel return connection being located vertically higher than the fuel inlet connection; a fuel supply line connected to the fuel inlet connection of each of the pods and a fuel return line connected to the fuel return connection of each of the pods such that the pods with the injectors inserted therein are connected in a parallel arrangement. 
     In the fuel injection system, each of the at least two injectors includes internal passageways fluidly communicating the at least one fuel inlet of the injector with the at least one vapor outlet of the injector. Preferably, an internal surface of each pod and an external surface of an injector inserted in the pod define a fluid passageway between the fuel inlet connection of the pod and the fuel return connection of the pod wherein the fluid passageway is external to the injector. 
     Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the following drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 schematically shows a top view of one embodiment of the fuel injection system according to the present invention. 
     FIG. 2 is a cross-sectional side view of one embodiment of a fuel injector and pod according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A fuel injection system according to the present invention insures rapid thorough flushing of the fuel injection valves and rapid cooling down of the fuel injection valves. Even under hot start conditions the necessary supply of fuel to the engine is assured and the engine starts and keeps running without interruptions, by means of rapid flushing of any fuel vapor that may be present out of the fuel injection valves and away from the injector valve seat. 
     A fuel injection system in accordance with the present invention includes a fuel injector pod that accommodates a fuel injector. The fuel injector may meter gasoline, liquid petroleum gas, or other high vapor pressure liquid petroleum and non-petroleum fuels. The fuel pod is connectable via a fuel rail to other pods to supply more than one cylinder of an engine. The pod efficiently purges vaporized fuel from liquid fuel. The efficient purging of the vaporized fuel maintains liquid fuel at the injector metering orifice, which provides stable and predictable metering of the fuel. 
     The pod improves hot engine restart by enabling fuel vapor bubbles to rise away from the fuel inlet and fuel metering components of a fuel injector. The rising fuel vapor bubbles escape the pod through a fuel return line located at a higher elevation than the fuel inlet. Liquid, being heavier than vapor, remains in the bottom of the pod near the fuel metering components due to gravity. 
     Fuel flows from the pod, which is external to the injector, to the interior of the injector through openings in the injector housing. The fuel flows internally through the injector to the metering orifice via passageways in the injector. Fuel also flows from the interior of the injector back to the pod via fuel purge vents in the injector housing. 
     A fuel rail having two passages is used with the pods. The lower passage is a fuel inlet passage that supplies liquid fuel to the lower part of the pod. The upper passage is a fuel vapor vent/fuel return passage that conducts vapor and excess fuel back to the fuel tank. 
     Fuel is supplied to each pod in parallel. That is, each pod is fed independently of each other pod so that the flow of fuel to a single pod does not restrict the flow of fuel to any other pod. In contrast to pods mounted in series at the end of a fuel feed line, the upstream pods do not starve the downstream pods in a parallel arrangement. The parallel arrangement helps to optimize vapor purging and minimize heat input to the fuel. 
     FIG. 1 schematically shows a top view of one embodiment of a fuel injection system  10  according to the present invention. The system  10  includes a plurality of pods  12  having bottom feed fuel injectors  14  inserted therein. A fuel pump  20  pumps fuel from a fuel tank  22  through a fuel supply line  16  to each pod  12 . Fuel vapor and liquid fuel return to the fuel tank  22  via a fuel return line  18 . The fuel supply line  16 , fuel return line  18  and pods  12  are connected in a parallel arrangement. The pods  12  are mounted on the intake air manifold (not shown). The pods are made of a material having low thermal conductivity. The pods  12  may be made of, for example, glass-filled nylon, plastic or a metal with low thermal conductivity. The pods  12  are usually formed by molding, but may be machined. 
     FIG. 1 shows four pods, however, the number of pods  12  may be any number greater than or equal to two. Each pod  12  with injector  14  inserted therein provides fuel to one cylinder (not shown) of an internal combustion engine. The fuel supply line  16  is located at a lower elevation than the fuel return line  18 . The difference in elevation causes the fuel vapor to rise to the fuel return line  18 . In FIG. 1, the supply line  16  and return line  18  are shown on opposite sides of the pods  12 . However, the supply and return lines  16 ,  18  can both be located on the same side of the pods  12  as long as the supply line  16  is at a lower elevation than the return line  18  and the lines are connected to the pods in a parallel arrangement. 
     FIG. 2 is a cross-sectional side view of one embodiment of a fuel injector  14  and pod  12  according to the present invention. The fuel injector  14  is inserted in an opening in the pod  12 . The pod  12  includes a fuel inlet connection  28  and a fuel return connection  30 . The fuel inlet connection  28  is lower in elevation than the fuel return connection  30 . One end  46  of the fuel inlet connection  28  is connected to the fuel supply line  16 . One end  48  of the fuel return connection  30  is connected to the fuel return line  18 . 
     The injector  14  includes at least one fuel inlet  24  and at least one vapor outlet  26 . The fuel inlet  24  is lower in elevation than the vapor outlet  26 . In a preferred embodiment, there are four fuel inlets  24  and two vapor outlets  26  arranged circumferentially around the injector  14 . Fuel is supplied to the injector  14  from the pod inlet connection  28  to the injector fuel inlet  24 . Fuel that is consumed by the engine passes by the needle valve  36  and out the injector tip  38 . Unused liquid fuel and fuel vapor bubbles flow through internal passageways in the injector  14  to the vapor outlet  26 . From the vapor outlet  26 , the fuel flows to the pod fuel return connection  30  to the fuel return line  18  and back to the fuel tank  22 . 
     One internal passageway that the unused fuel and fuel vapor bubbles may take is upwards past the needle valve  36  to the armature  32 . The armature  32  contains openings through which the fuel may pass. The fuel then flows around the electric coils  34  to one or more vapor outlets  26 . 
     In one embodiment, fuel may also flow from the pod fuel inlet connection  28  to the pod fuel return connection  30  via a passageway  44  that is external to the injector  14 . The passageway  44  is defined by an internal surface  40  of the pod  12  and an external surface  42  of the injector  14 . The external passageway  44  allows vapor bubbles to flow directly from the fuel inlet  28  to the vapor outlet  26 . The external passageway  44  may extend circumferentially around the entire injector  14  thereby attaining a generally annular shape. 
     While the invention has been described with reference to certain preferred embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.