Fuel/air supply system for a fuel injector and methods of operation

TECHNICAL FIELD

The present invention relates generally to a fuel and air supply system for fuel injectors and particularly relates to a system for supplying fuel and air to a fuel injector over a predetermined time interval whereby a fuel/air dispersion can be effected through the orifice of the fuel injector, e.g., at engine start-up, and to methods of operating the fuel/air supply system.

BACKGROUND

Fuel injectors typically comprise an electromagnetically actuated needle valve disposed in a fuel volume and which needle valve is reciprocated axially within the fuel volume in response to energization and deenergization of an actuator to selectively open and close a flow path through the fuel injector. Particularly, the valve body or housing defining the fuel volume has an aperture or orifice at one end about which is formed a seat for the end of the needle valve whereby reciprocating motion of the needle valve enables an intermittent flow of fuel through the orifice. Fuel emitted from a fuel injector is typically atomized downstream of the orifice to provide the necessary fuel/air mixture in the combustion chamber of the engine.

US-A-4 157 084 discloses a fuel injector system for an internal combustion engine in which an improved startup system is provided. During startup, a thoroughly mixed quantity of air and highly atomized fuel is injected into the engine to minimize fuel waste and produce minimum pollutants. The system comprises an electrically controlled fuel injector valve which is connected to receive a supply of premixed fuel and pressurized air from a mixing device. The mixing device is connected to receive fuel from a main fuel supply line and pressurized air from an air compressor which may be powered by the engine or by a separate motor.

In a companion application by the present inventors (USSN 08/686,939 filed July 26, 1 996 and entitled Fuel Injector With Air Bubble/Fuel Dispersion Prior to Injection and Methods of Operation), there is provided a fuel injector in which an air bubble/fuel dispersion is provided within the fuel volume of a fuel injector upstream of the injector orifice. This is accomplished by supplying air under pressure through one or more porous members situate in an air inlet in communication with the fuel volume upstream of the orifice. The air flows through the porous member and forms bubbles of a predetermined size in the fuel within the fuel volume. The bubbles are sized by the pore size of the porous member such that the air bubbles dispersed in the fuel in the fuel volume do not substantially rise. Consequently, a predetermined mass of a two-phase air bubble/fuel dispersion can be ejected through the orifice of the fuel injector for improved atomization, fuel economy and burn with resulting lower emissions. The present invention provides novel and improved apparatus and methods for supplying fuel and air to a fuel injector of that type and over a predetermined time interval.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention, there is provided a fuel injector system for supplying a two-phase air/fuel dispersion to an engine comprising:- a fuel injector having an orifice, a fuel volume upstream of said orifice and a valve for opening and closing said orifice; and a fuel supply line connected to said fuel injector for supplying fuel to said fuel volume; characterised in that said fuel injector further comprises an air inlet to said fuel volume having a porous member for admitting air into said fuel volume to cause the formation of air bubbles in the fuel in said fuel volume; and in that said system further comprises:- a pressure reducer in said fuel supply line upstream of said fuel volume for supplying fuel to said fuel volume at a pressure lower than a fuel supply line pressure upstream of said pressure reducer; an air reservoir in communication with said air inlet for supplying air to said inlet at a pressure higher than the pressure of the fuel supplied to said fuel volume; and a bypass line coupled between said air reservoir and said fuel supply line at a location upstream of said pressure reducer for supplying fuel to said air reservoir at a pressure corresponding to the supply line pressure upstream of said pressure reducer thereby enabling flow of air to said air inlet at a higher pressure than the pressure of the fuel in said fuel volume and the formation of an air bubble/fuel dispersion in said fuel volume upstream of the fuel injector orifice.

According to another aspect of the present invention, there is provided a method of supplying fuel and air to an injector in a fuel injection system as described above, the method comprising the steps of:- flowing fuel to said air reservoir at a first pressure to pressurize air in said reservoir; flowing fuel to said fuel volume of said fuel injector at a second pressure less than said first pressure; and flowing the pressurized air from said air reservoir to said air inlet at a pressure substantially corresponding to said first pressure thereby establishing a pressure differential across said porous member and flow of air through said member and flow of air through said member into said fuel volume.

In accordance with the present invention, fuel is supplied from a fuel pump at a first or line pressure and through a pressure reducing element, e.g., for supplying fuel at a reduced or lower pressure directly to the fuel injector. Upstream of the pressure reducing element, a bypass line is coupled between the fuel supply line and an air reservoir. Fuel is thus supplied from the fuel pump into the air reservoir and at the first pressure. The air reservoir is in turn in communication with the air inlet of the fuel injector. Air is therefore supplied from the air reservoir at the line or first pressure to the air inlet and through the porous member to form the air bubbles in the fuel in the fuel volume of the injector at a location upstream of the orifice. The air reservoir includes an air valve normally open to the atmosphere or another air source and which air valve can be mechanically or electrically operated to close, e.g., upon pressurization of the air reservoir. The air reservoir also has a normally open fuel valve which is likewise operated, e.g., to close in response to pressurization of the air reservoir. The fuel valve lies in communication with a fuel tank which, of course, supplies fuel to the fuel pump.

To operate the fuel/air supply system for the fuel injector, for example, upon engine start-up, fuel at the first pressure is supplied to the air reservoir, pressurizing the air in the reservoir. The air and fuel valves in the air reservoir, when pressurized, are closed. Fuel is also supplied through the pressure reducing element directly to the fuel inlet for the fuel injector at a lower pressure than the first pressure. As a consequence, air in the air reservoir attains the fuel supply line pressure, i.e., the first pressure, and establishes a pressure difference across the porous member or members in the fuel injector. This pressure difference causes the air to pass through the porous member into the fuel in the fuel volume in the form of small discrete bubbles 40 microns or less in size to form the air bubble/fuel dispersion. This dispersion is intermittently injected into the combustion engine by periodic operation of the needle valve opening and closing the fuel injector orifice.

It will be appreciated that the air reservoir will eventually fill with fuel including the air line to the porous member(s) of the fuel injector. However, because the porous member(s) are substantially impermeable to fuel, fuel from the air reservoir when filled will not pass through the porous member. When the fuel pump is deenergized, for example, when the engine is turned off, both the fuel valve connecting the air reservoir to the fuel tank and the air valve between the air reservoir and atmosphere or another source of air are opened. This may be accomplished electrically in response to engine shutdown or mechanically in response to atmospheric or another pressure in the air reservoir. By opening the valves, air at reduced pressure is supplied to the air reservoir and the fuel in the air reservoir flows to the fuel tank of the engine, effectively emptying the air reservoir.

Given a particular size of air reservoir and a given pressure difference across the pressure reducer, it will be appreciated that air will be supplied to the air inlet of the injector for a predetermined period of time, after which air will no longer be supplied to the fuel injector. At that time and thereafter, only fuel will pass through the orifice of the injector in a conventional manner. Consequently, the system is particularly effective at engine start-up to provide improved atomization of the fuel to the engine with subsequent conventional operation of the injector. The system is also self-regulating by returning the air reservoir to its normal condition substantially void of fuel. Thus, the engine can be restarted with the air reservoir supplying air to the fuel injector, again enabling an air bubble/fuel dispersion to be injected through the orifice of the injector into the engine upon start-up.

Accordingly, it is a primary object of the present invention to provide a novel and improved air and fuel supply system for a fuel injector having improved atomization characteristics and methods of operating the system.

BRIEF DESCRIPTION OF THE DRAWNGS

• FIGURE 1 is a longitudinal cross-sectional view of a fuel injector for use with a fuel/air supply system constructed in accordance with the present invention; and
• FIGURE 2 is a schematic diagram of the fuel/air supply system hereof for supplying fuel and air to the fuel injector illustrated in Figure 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to Figure 1, there is illustrated a fuel injector. constructed in accordance with our invention as set forth in companion patent application Serial No. 08/686,939, filed July 26, 1996 of common assignee granted as US-Patent 5,730,367, the subject matter of which is incorporated herein by reference. In accordance with that invention, there is provided a fuel injector, generally designated 10, including a housing assembly 12 mounting a coil assembly 14 and an armature 16 coupled to a needle valve 18. Surrounding the needle valve 18 is a housing 22 defining a fuel volume 24 in communication with a fuel flow passage 20 through the armature. At the lower end of housing 22 is a valve seat 26 defining an orifice 28 through which an air bubble/fuel dispersion is ejected from the fuel injector into the engine as set forth in the previously described companion application. It will be appreciated that the coil 14 and armature 16 cooperate to open and close orifice 28 by periodic axial movement of needle valve 18 within fuel volume 24.

In accordance with the invention of that companion application, one or more porous members 30 are provided in an air inlet 32 in communication with the fuel volume 24. By providing air at a higher pressure than the pressure of the fuel in fuel volume 24, and a pore size in the porous member sufficiently small, e.g., 40 microns or less, air bubbles are provided in the fuel in the fuel volume of a size which do not substantially rise within the fuel volume. In this manner, a constant known mass of fuel can be injected into the engine upon opening the orifice 28 by actuation of the needle valve 18.

Referring now to Figure 2, a fuel and air supply system according to the present invention is illustrated. Particularly, there is provided a fuel tank 40 in communication with a fuel pump 42 for supplying fuel under a first pressure to a fuel supply line 44. A pressure reducing element 46, e.g., a restrictor or pressure regulator, is disposed in the fuel supply line 44 for supplying fuel directly to the fuel injector 10 at a second reduced pressure, for example, through a fuel feed line 48, for flow into the fuel volume 24 via passage 20.

An air reservoir 50 is also provided and lies in communication via a line 52 with the air inlet 32 of injector 10. The air inlet 32 may comprise an annular manifold about the injector in communication with one or more ports 31 opening into fuel volume 24. Air line 52 supplies air to the air inlet 32 of the injector at a pressure higher than the pressure of the fuel supplied to the fuel volume 24 via feed line 48. To accomplish this, a fuel bypass line 54 communicates between fuel supply line 44 and reservoir 50. From a review of drawing Figure 2, it will be appreciated that the bypass line 54 communicates with the fuel supply line 44 upstream of the pressure reducing element 46. Consequently, fuel is supplied at the first pressure to the air reservoir 50, while fuel is supplied to the fuel injector and fuel volume 24 at a reduced pressure via line 48. Air reservoir 50 is provided with a fuel return line 56 for returning fuel supplied to air reservoir 50 from the fuel supply line 44 and bypass line 54 to the fuel tank 40. A first normally open fuel valve 58, which may be mechanically or electrically operated, e.g., in response to a predetermined pressure in the air reservoir or engine start-up, is provided. A second, normally open air valve 60 is provided, preferably adjacent the upper end of air reservoir 50. Valve 60 may similarly be mechanically or electrically operated to close in response to a pressure within the air reservoir 50 in excess of the predetermined air pressure or to engine start-up. Both valves return to their normally open positions when the system is not in use, e.g., in response to depressurization of the air reservoir or engine shutdown.

To operate the fuel and air supply system hereof, the air reservoir, with the engine off, contains a predetermined air pressure, for example, and preferably atmospheric pressure, with valves 58 and 60 open. Fuel valve 58 is normally open such that any fuel in the air reservoir drains to the fuel tank 40, and air valve 60 is normally open, preferably such that the air reservoir is at atmospheric pressure. At start-up, fuel pump 42 supplies fuel from the fuel tank 40 under pressure via supply line 44 to both the fuel injector and the air reservoir. The fuel supplied to the fuel injector is at a pressure reduced from or lower than the pressure of the fuel in supply line 44. Fuel is also supplied via line 54 to the air reservoir at a pressure corresponding to the pressure of fuel supply line 44 thereby increasing the air pressure within the air reservoir 50. This increase in air pressure may close the normally open valves 58 and 60 or they may be electrically actuated to close in response to engine start-up, e.g., energization of the fuel pump. Thus, the air pressure in air reservoir 50 corresponds to the pressure of the fuel supplied to the air reservoir 50 from fuel supply line 44. It will be appreciated that the air supplied to the air inlet 32 of the injector via the air reservoir 50 and air supply line 52 will therefore be at a higher pressure than the pressure of the fuel in fuel volume 24. Air will therefore pass through the porous member into the fuel volume, creating a two-phase air bubble/fuel dispersion in the fuel. Consequently, the dispersion flows through the orifice 28 upon opening valve 18.

Upon starting the engine, it will be appreciated that fuel continues to flow via the bypass line 54 into the air reservoir until such time as the reservoir and air line 52 are filled with fuel under the first pressure. When the fuel reaches the porous member(s), the air reservoir 50 and line 52 are completely filled with fuel and air is no longer supplied to the fuel volume. The fuel injector thereafter operates in a normal manner, i.e., fuel is sprayed through the orifice for downstream atomization and ingress into the engine without prior atomization in the fuel volume.

When the engine is shut off, the fuel pump 42 discontinues pressurizing the fuel in line 44. The air reservoir is thus depressurized and the valves 58 and 60 open to permit outflow of fuel from air reservoir 50 into the fuel tank 40 and inflow of air at a predetermined pressure, respectively, into the air reservoir. Consequently, the air reservoir is substantially emptied of fuel, and replaced by air at a predetermined, preferably atmospheric, pressure. Upon restarting the engine, the cycle is repeated, whereby the air bubble/fuel dispersion is provided in the fuel volume of the injector for ejection through the orifice 28 only for a predetermined time until the reservoir 50 and line 52 fill with fuel. At that time, atomization of the fuel prior to injection through the orifice 18 is discontinued while fuel continues to be injected through orifice 18.

As a specific example of the operation of the system, the pressure reducing element 46 may provide a 10% pressure drop in the fuel flow. Consequently, if fuel is supplied via line 44 at 300kPa, the fuel is supplied to the fuel injector at 270kPa, while fuel is provided to the air reservoir 50 at 300kPa. Consequently, a 30kPa pressure differential appears across the porous member(s). This pressure difference and consequent air flow from the air reservoir through the porous member(s) will continue for a period of time, controlled by the pressure difference and the volume of air in the reservoir. Once the air is displaced, the fuel filling the air reservoir and line 52 precludes further injection of air into the fuel volume.