Abstract:
A dual-fuel system, comprising an electrically triggerable injector, for alternatively or simultaneously supplying two distinct fuels to an internal combustion engine. The injector is connected to two separate fuel circuits. Each circuit comprises a fuel storage tank and a fuel rail. External valves control fuel access from the fuel storage tanks to the fuel rails. By appropriately activating the valves, one or both of the two fuels are fed to the injector. Inside the injector are two separate fuel paths, fluidically isolated from each other. Each internal fuel path communicates with one of the external fuel circuits. The injector contains a flow control valve for each separate fuel path and one electromagnet. In the non-activated position, both valves are resiliently urged against a common seat. When the electromagnet is energized, it simultaneously drives the two valves to open off the seat, thereby permitting one or two fuels to pass therethrough.

Description:
This application claims benefit under 37 CFR 119e to the provisional application No. 60/210,084 filed Jun. 7, 2000. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     REFERENCE TO MICROFICHE APPENDIX 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     This invention relates to fuel systems for internal combustion engines and more particularly to a fuel injection system whereby two distinct fuels are used, either alternatively or simultaneously. 
     With ever more stringent emissions regulations, the use of alternative gaseous fuels for operating internal combustion engines has become increasingly attractive. The more commonly used gaseous fuels are compressed natural gas (CNG) and liquefied petroleum gas (LPG). These gases can burn cleaner than gasoline and the cost per unit of energy is lower. 
     A majority of the end users are specifically requesting dual fuel systems, capable to run on gasoline or a gaseous fuel, such as CNG or LPG. While factory installed gaseous or dual fuel systems are available today, in many cases, the gaseous fuel system is still a retrofit complementing the original gasoline fuel system. 
     Another possible application for a dual fuel system is the use of methanol fuel as an alternative to, or in combination with, gasoline. In some countries, methanol is readily available and cost-effective. The use of a mixture of gasoline and methanol has certain advantages but it is difficult to implement, because the two liquids do not mix well. 
     The last decade has witnessed the migration of the automotive engine fuel system from carburetors to port fuel injection, using one fuel-metering device, in the form of a fuel injector, for each engine cylinder. This migration has been driven by the numerous drawbacks associated with central mixture preparation. Carburetors create a significant restriction in the intake air path, thereby impairing the volumetric efficiency of the engine. Furthermore, central mixture preparation entails air-fuel ratio maldistribution among the different cylinders of the engine, with negative consequences on the exhaust emissions. 
     Although virtually all of the modern automotive gasoline fuel systems are of the port fuel injection type, many of the dual fuel, liquid and gas, systems still resort to a centrally located air—fuel mixing device for supply and metering of the gaseous fuel. This central mixture preparation device most often consists of some variety of a carburetor. A few systems use central fuel injection instead. 
     A lot of effort has been made in the last few years to develop advanced port injection gaseous fuel systems. Gaseous variants of the gasoline port fuel injection have been developed for dedicated, gas only, applications. 
     Design of simple and reliable dual fuel port injection systems has been less successful. Most prior art dual fuel systems which do utilize injectors for both fuels use two separate injectors, one for each of the fuels (such as described by U.S. Pat. No. 5,755,211—Koch, or U.S. Pat. No. 5,713,336—King et al). Some of the disadvantages of this solution are: 
     Two separate fuel rails are used, cluttering the system and complicating installation. 
     Doubles the number of injectors in the system, compared to a single fuel application. 
     A second electronic control unit (ECU) is required to drive the gaseous fuel sub-system. 
     Attempts have been made to integrate the delivery of both fuels into one single injector device (U.S. Pat. No. 5,887,799—Smith). Some of the disadvantages of the solution proposed by the author of U.S. Pat. No. 5,887,799 are: 
     The impossibility to deliver both fuels at the same time. 
     The fuel rails are positioned at both ends of the injector, making installation difficult. 
     The need for a special injector driver that can reverse pulse polarity. 
     Other single—injector designs utilized for dual fuel, liquid—liquid injection, rely solely on injector pulse signal modulation to accommodate for the different fuels. This technique is not applicable to most dual fuel, liquid—gas systems, where the energy density of the gaseous fuel is typically much lower than the liquid&#39;s. 
     BRIEF SUMMARY OF THE INVENTION 
     The device of the invention overcomes the aforementioned disadvantages of the prior art by utilizing a single fuel injector to supply two distinct fuels to an internal combustion engine. The injector is fluidically connected to two separate external fuel circuits, one for each of the two distinct fuels. 
     Each external fuel circuit comprises a fuel storage tank, a fuel pressure regulator and a fuel rail. In the preferred embodiment, the two fuel rails are coaxial, which makes packaging identical to a gasoline fuel injection system. Fuel access from the storage tanks to the fuel rails is controlled by an arrangement of valves. The two external fuel circuits are fluidically isolated from each other. 
     The injector has two separate internal fuel circuits, with at least one fuel flow control valve in each circuit. Each internal fuel circuit is fluidically connected to one of the fuel rails and isolated from the other fuel circuit. 
     In the preferred embodiment, the two fuel control valves are simultaneously driven by an electromagnet and feed of a desired fuel is achieved by selectively connecting one or the other of the fuel rails to the desired fuel storage tank. 
     OBJECTS AND ADVANTAGES 
     Accordingly, Several Objects and Advantages of My Invention are 
     Ease of installation on the engine, since the fuel rails and injectors are similar in shape and size to the same components of a gasoline fuel injection system. 
     In the most common application, the conversion of a fuel injected gasoline engine to bi-fuel operation, on gasoline and a gaseous fuel, the fuel system of the invention does not entail any modifications of, or restrictions in, the engine intake air duct, thereby preserving the original gasoline engine performance and maximizing the performance potential for the gaseous fuel. 
     The fuel system, according to the invention, eliminates the need for a separate controller for the second fuel sub-system. 
     The possibility to run two distinct fuels simultaneously with one injector. 
     The possibility to use more than just two different fuels: i.e. compressed natural gas (CNG) and liquefied propane gas (LPG) could alternatively use the same rail—but two distinct tanks—and the system would be a triple fuel one. 
     The fuel system, according to the invention, can be used for bi-phase, liquid or gas, LPG fuelling. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a schematic representation of the fuel system of the invention; 
     FIG. 2 is a detailed cross-sectional view through the fuel rails and injectors; 
     FIG. 3 illustrates a preferred embodiment of the installed injector, according to the invention, in its neutral, non-activated position; 
     FIG. 4 is a schematic illustration showing the fuel system, according to the invention, operating in its mode for feeding a main fuel; 
     FIG. 4A shows a preferred embodiment of the injector, according to the invention, operating on a main fuel; 
     FIG. 5 is a schematic illustration showing the fuel system, according to the invention, operating in its mode for feeding a secondary fuel; 
     FIG. 5A shows a preferred embodiment of the injector, according to the invention, operating on a secondary fuel; 
    
    
     LIST OF REFERENCE NUMERALS 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 11 
                 Main Fuel Storage Tank 
               
               
                   
                 12 
                 Main Fuel Pump 
               
               
                   
                 13 
                 Main Rail Inlet Valve 
               
               
                   
                 14 
                 Main Fuel Rail 
               
               
                   
                 15 
                 Main Fuel Pressure Regulator 
               
               
                   
                 16 
                 Secondary Fuel Storage Tank 
               
               
                   
                 17 
                 Secondary Fuel Pressure Regulator 
               
               
                   
                 18 
                 Secondary Rail Inlet Valve 
               
               
                   
                 19 
                 Secondary Fuel Rail 
               
               
                   
                 20 
                 Dual Fuel Injector 
               
               
                   
                 21 
                 Engine Intake Air Duct 
               
               
                   
                 22 
                 Main Fuel Inlet 
               
               
                   
                 23 
                 Secondary Fuel Inlet 
               
               
                   
                 24 
                 Main Fuel Passage 
               
               
                   
                 25 
                 Secondary Fuel Passage 
               
               
                   
                 26 
                 Injector Body 
               
               
                   
                 27 
                 Electromagnet 
               
               
                   
                 28 
                 Electromagnet Core 
               
               
                   
                 29 
                 Electromagnet Coil 
               
               
                   
                 30 
                 Common Valve Seat 
               
               
                   
                 31 
                 Nozzle 
               
               
                   
                 32 
                 Internal O-Ring 
               
               
                   
                 33 
                 Main Fuel Discharge Passage 
               
               
                   
                 34 
                 Secondary Fuel Discharge Passage 
               
               
                   
                 35 
                 Main Fuel Atomizing Orifice 
               
               
                   
                 36 
                 Main Metering Orifice 
               
               
                   
                 37 
                 Secondary Metering Orifices 
               
               
                   
                 38 
                 Main Fuel Valve 
               
               
                   
                 38A 
                 Axial Transfer Duct 
               
               
                   
                 38B 
                 Radial Transfer Duct 
               
               
                   
                 39 
                 Main Stroke Limiter 
               
               
                   
                 40 
                 Secondary Fuel Valve 
               
               
                   
                 40A 
                 Secondary Fuel Transfer Port 
               
               
                   
                 41 
                 Secondary Stroke Limiter 
               
               
                   
                 42 
                 Secondary Return Spring 
               
               
                   
                 43 
                 Main Return Spring 
               
               
                   
                 44 
                 Electrical Connector 
               
               
                   
                 45 
                 Electrical Terminals 
               
               
                   
                 46 
                 External O-Ring 
               
               
                   
                 47 
                 Separating O-Ring 
               
               
                   
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION OF THE INVENTION 
     In the preferred embodiment, the fuel system uses a liquid main fuel and a gaseous secondary fuel. 
     FIG. 1 shows a schematic illustration of a preferred embodiment of the dual fuel system, according to the invention. The system depicted by FIG. 1 comprises a main fuel section and a secondary fuel section. The main fuel section comprises a main fuel storage tank  11 , a main fuel pump  12 , a main rail inlet valve  13 , a main fuel rail  14  and a main fuel pressure regulator  15 . The secondary fuel section comprises a secondary fuel storage tank  16 , a secondary pressure regulator  17 , a secondary rail inlet valve  18  and a secondary fuel rail  19 . A plurality of dual fuel injectors  20  are attached and fluidically connected to both fuel rails. The injectors extend into an engine air intake duct  21 . 
     In a preferred embodiment, main fuel rail  14  is coaxially mounted inside secondary fuel rail  19 , as illustrated in FIG.  1  and FIG.  2 . 
     Referring now to the cross-sectional view in FIG. 3, a preferred embodiment of the installed injector is illustrated. As shown in this figure, the injector is in its neutral mode, neither the main nor the secondary fuel feeds being activated. 
     The injector has a main fuel inlet  22 , which fluidically connects the injector to main fuel rail  14 . Surrounding main fuel inlet  22  is a secondary fuel inlet  23 , which fluidically connects the injector to secondary fuel rail  19 . At least one main fuel passage  24  is machined through main fuel inlet  22 . At least one secondary fuel passage  25  is machined through secondary fuel inlet  23 . 
     Both main and secondary fuel inlets are fixedly mounted into an injector body  26 . Also fixedly mounted in the injector body are an electromagnet  27  comprising an electromagnet core  28  and an electromagnet coil  29 , a common valve seat  30 , and a nozzle  31 . An internal o-ring  32  provides a fluid tight seal between common valve seat  30  and nozzle  31 . In the preferred embodiment, main fuel inlet  22  also serves as a magnetic core to electromagnet  27 . 
     There is at least one main fuel discharge passage  33  machined through nozzle  31 . 
     Surrounding main fuel discharge passage  33  is an annular secondary fuel discharge passage  34 . In the absence of an annular passage there may be a plurality of circular holes, arranged in a circular pattern and serving the same purpose. 
     The nozzle end opposite to the common seat is permanently open to communicate with the internal combustion engine intake air duct, for both the main and the secondary fuel discharge passages. In the preferred embodiment, a main fuel atomizing orifice  35  is placed at the open end of main fuel discharge passage  33 . 
     Common valve seat  30  has at least one centrally located main metering orifice  36  and at least one secondary metering orifice  37 . In the preferred embodiment, there is a plurality of secondary metering orifices  37 , arranged in a circular pattern surrounding the centrally located main metering orifice. 
     A main fuel valve  38  is slidably mounted in the injector body, between common valve seat  30  and electromagnet core  28 . The main fuel valve has an axial transfer duct  38 A, which communicates with a plurality of radial transfer ducts  38 B. 
     Surrounding the main fuel valve is a main stroke limiter  39 . The stroke limiter is fixedly mounted between electromagnet core  28  and common valve seat  30 . Means are provided to ensure a fluid tight seal between main stroke limiter  39  and adjoining electromagnet core  28  and common valve seat  30 . 
     Surrounding main stroke limiter  39  and slidably mounted between electromagnet core  28  and common valve seat  30 , is a secondary fuel valve  40 . The secondary fuel valve is cup-shaped and has at least one secondary fuel transfer port  40 A. In the preferred embodiment, there is a plurality of radially arranged secondary fuel transfer ports  40 A. The cup shape of the secondary fuel valve, in combination with the fuel transfer ports equalize fuel pressure between the space inside and the space outside the valve, whereby reducing the force required to open the valve. 
     A secondary stroke limiter  41  is fixedly mounted inside injector body  26  and has the role to limit the secondary fuel valve travel. 
     Secondary fuel valve  40  and main fuel valve  38  are resiliently urged to their closed position, against common valve seat  30 , by a secondary return spring  42  and a main return spring  43 , respectively. Thus, a fluid tight seal is provided between the fuel valves and the common seat. 
     An electrical connector  44  is fixedly attached to injector body  26 . The connector positively locates the fixedly mounted components into the injector body and seals the injector from the surroundings. Inside the connector are a plurality of electrical terminals  45 , electrically connected to electromagnet coil  29 . 
     An external o-ring  46  provides a fluid tight seal between secondary fuel inlet  23  and the surroundings, while a separating o-ring  47  fluidically isolates the main fuel rail from the secondary fuel rail. 
     Operation 
     Referring to FIG. 4 and 4A, the use of the device of the invention for feeding a main fuel is illustrated. As shown in FIG. 4, main rail inlet valve  13  is open and main fuel pump  12  is energized, thereby allowing a main fuel to flow from main fuel storage tank  11  into main fuel rail  14 . 
     Main fuel pressure regulator  15  keeps the main fuel at a substantially constant pressure in the main fuel rail. Secondary rail inlet valve  18  is closed. Since only the main fuel rail contains a fuel under pressure, only a main fuel is allowed to pass from main fuel rail  14  into injectors  20 . 
     Referring now to FIG. 4A, the pressurized main fuel flows through injector internal main fuel passage  24 , axial transfer duct  38 A, and radial transfer ducts  38 B. The fuel flow stops at the main fuel valve, which, in its non-activated position is resiliently urged against common seat  30  by main return spring  43 , thereby providing a fluid tight seal at the common seat. 
     When electrical pulses are fed to electromagnet  27 , main fuel valve  38  and secondary fuel valve  40  are caused to simultaneously lift off common valve seat  30  and against the spring action of main and secondary return springs, respectively. 
     Main fuel valve  38  thereby opens and stays open for the duration of the electrical pulse, permitting the main fuel to flow through main metering orifice  36 , main fuel discharge passage  33 , and finally out through main fuel atomizing orifice  35 . Main stroke limiter  39  provides for a substantially constant main valve travel, therefore the fuel quantity delivered in one pulse depends only on the pulse duration. 
     Referring to FIG. 5 and 5A, the use of the device of the invention for feeding a secondary fuel is illustrated. As shown in FIG. 5, when secondary fuel delivery is required, secondary rail inlet valve  18  is open, thereby allowing a secondary fuel to flow from secondary fuel storage tank  16  through secondary fuel pressure regulator  17  and into secondary fuel rail  19 . The secondary fuel pressure regulator maintains a substantially constant fuel pressure in the secondary fuel rail. Main rail inlet valve  13  is closed. Since only the secondary fuel rail contains a fuel under pressure, a secondary fuel only is allowed to pass from the secondary fuel rail into injectors  20 . 
     Referring now to FIG. 5A, the pressurized secondary fuel flows through the injector internal secondary fuel passages  25 , around electromagnet  27  and through secondary fuel transfer port  40 A. The fuel flow stops at the secondary fuel valve, which, in its non-activated position is resiliently urged against common seat  30  by secondary return spring  42 , thereby providing a fluid tight seal at the common seat. 
     Electrical pulses are fed to electromagnet  27 , causing main fuel valve  38  and secondary fuel valve  40  to simultaneously lift off common valve seat  30 , against the spring action of the main and secondary springs, respectively. Secondary fuel valve  40  thereby opens and stays open for the duration of the electrical pulse, permitting the secondary fuel to flow through secondary metering orifice  37  and finally out through secondary fuel discharge passage  34 . Secondary stroke limiter  41  provides for a substantially constant secondary valve travel, therefore the fuel quantity delivered in one pulse depends only on the pulse duration. 
     As both main and secondary fuel valves open simultaneously, even when the system supplies just one of the two fuels, all of the fuel that may be trapped in the currently unused circuit is rapidly purged into the engine, thereby avoiding fuel deposits in the unused circuit. Additionally, continuous functioning of both valves prevents the currently unused valve from binding to its seat. 
     Conclusion, Ramifications and Scope 
     Thus the reader will see that the fuel system of the invention provides a simple yet effective solution for feeding an internal combustion engine with two distinct fuels, either alternatively or simultaneously. When converting a fuel injected spark ignition engine to bi-fuel functioning, the fuel system of the invention permits easy mounting on the engine, with little or no changes to the intake manifold. All the original electrical and electronic hardware is retained, the only changes required by the bi-fuel functioning occurring in software. Since no restrictions are added to the intake air path, in a gasoline-gaseous fuel bi-fuel application, the system maintains engine performance on gasoline while maximizing performance on the gaseous fuel. 
     While my description contains many specificities, these should not be considered as limitations on the scope of the invention, but rather as an exemplification of one preferred embodiment thereof. Many other variations are possible. For example: 
     An alternative embodiment uses two electromagnets, one for each metering valve. 
     Another alternative embodiment achieves fuel metering by means of calibrated orifices located downstream of the fuel control valves, preferably in the nozzle. 
     While the preferred embodiment illustrates a typical port fuel injection system, a different embodiment of the same device may be designed to operate as a central, or throttle body, fuel injection system. 
     Accordingly, the scope of the invention should be determined not by the embodiment illustrated, but by the appended claims and their legal equivalents. 
     LIST OF REFERENCE NUMERALS 
       1  Fuel Inlet 
       2  Fuel Passage 
       3  Fuel Port 
       4  Body 
       5  Solenoid 
       6  Nozzle 
       7  Electrical insulator 
       8  First Electrode 
       9  Valve Seat 
       10  Fuel Discharge Cavity 
       11  Combustion Shell 
       12  Combustion Chamber 
       13  Second Electrode 
       14  Torch nozzle 
       15  Pilot Injection Port 
       16  Main Injection Port 
       17  Valve 
       17 A Valve Stem 
       17 B Locating Collar 
       18  Fuel Passage Groove 
       19  Stroke Limiter 
       20  First Spring Retainer 
       21  Return Spring 
       22  Second Spring Retainer 
       23  Armature 
       24  Electrical connector 
       25  Electrical terminals