IN TANK FUEL PUMP

Abstract: A fuel pump locatable within a fuel tank including: a fuel pump housing (1); a pumping mechanism (5) located within the housing (1) for pumping fuel; an electric motor (3) for driving the pumping mechanism (5), the motor (3) being accommodated within a motor cavity (10) with the housing (1); a fuel inlet for the pumping arrangement; wherein the fuel pump housing (1) includes a breather arrangement (2) for allowing air and fuel vapor within the cavity (10) to escape therefrom when displaced by fuel passing into the motor cavity (10).

Description: IN TANK FUEL PUMP The present invention is generally directed to fuel pumps for supplying fuel to an internal combustion engine, and in particular to fuel pumps suitable for location within a fuel tank. There are two main types of fuel systems commonly used to supply fuel to an internal combustion engine of a vehicle such as automobiles, motorcycles, scooters, boats and aircraft. These fuel systems are carburetor based fuel systems and injector based fuel systems. Carburetor based fuel systems can provide an air/fuel mixture to an inlet manifold of an engine, with fuel being drawn by the carburetor from a fuel tank through a fuel conduit extending into the tank. As the carburetor provides a vacuum within the conduit and as the conduit can be located with its end adjacent the bottom of the tank the fuel tank can commonly be almost fully emptied by a carburetor. Injector based fuel systems, and in particular direct injection fuel system, require fuel pumps in order to supply fuel at an elevated pressure to the fuel injectors. Fuel pumps may be driven by an electric motor, and may be conveniently located within a fuel tank. In many of these so called "in-tank" fuel pumps, the electric motor of the pump, and in particular the commutator and brush of the electric motor are arranged so as to be flooded by the fuel held within the tank as this helps to prevent sparks being generated between the commutator and brush of the motor while it is running. The Applicant has developed fuel injection systems for small engine applications. An example of a small engine application is a motor-scooter having an engine with a capacity in the range of about 50cc to 100cc. It is preferable under these circumstances to have a relatively inexpensive fuel pump with a small current draw while at the same time providing sufficient pressure for a fuel injection system, particularly direct injection fuel systems that require fuel to be supplied at higher pressures than manifold (or port) injection systems. Typical in-tank pumps do not however provide such a combination of features and typically draw too high a current (in the order of 1.5A or greater) and hence represent a significant parasitic loss to a small engine application employing a fuel injection system. Alternatively pumps that have low power draw typically supply fuel at insufficient pressure for effective operation of a fuel injection system. One type of pump which provides such features incorporates an elongate piston driven in a reciprocal movement by a cam and follower arrangement or by a linear slider mechanism. Such a pump is described in the Applicant's International Application No. PCT/AU99/00601 , details of which are incorporated herein by reference. The described pump is however particularly adapted for use as an "in-line" pump and has a fully sealed housing for the electric motor. Such a pump cannot be located in use in a fuel tank because the electric motor is not housed sufficiently for it to be safely flooded by fuel. Another problem with many existing in-tank fuel pumps is that their construction is such that they are unable to completely empty the fuel tank and so leave residual fuel in the tank. This limits the maximum range of a vehicle as it is unable to gain access to all of the fuel within the fuel tank. For small engine applications that have low capacity fuel tanks, this residual fuel can represent a significant percentage of tank capacity. It is therefore an object of the present invention to provide a fuel pump locatable within a fuel tank that overcomes at least one of the problems associated with known fuel pumps. With this is mind, there is provided an fuel pump locatable within a fuel tank including: a fuel pump housing; a pumping mechanism located within the housing for pumping fuel; an electric motor for driving the pumping mechanism, the motor being accommodated within a motor cavity within the housing; a fuel inlet for the pumping arrangement; wherein the fuel pump housing includes a breather arrangement for allowing air and fuel vapour within the cavity to escape therefrom when displaced by fuel passing into the motor cavity. Preferably the breather operates as a filter. Preferably the breather provides impedance to air flow into and out of the motor cavity after priming of the pump. The provision of a breather arrangement enables the motor cavity to be flooded with fuel when the fuel pump is located in a tank and fuel is admitted to the tank so as to reach a level that submerges the motor cavity. The fuel may enter through a fuel inlet of the pump and pass or percolate through the pumping mechanism and the electric motor and thereby force air trapped in the pump housing / motor cavity through the breather. Accordingly it is preferable that the fuel inlet is positioned below the breather when the pump is located for use within a fuel tank. This enables the breather to assist with priming the pump. The breather arrangement may be in the form of a sintered breather plate or disc. This sintered breather may be located above the motor in a position that is either co-extensive with or adjacent an aperture in the fuel pump housing or may be located in an end cap separable from the rest of the housing when the fuel pump is located into its "in use" orientation. The remainder of the housing is preferably sealed so that the breather forms the primary mechanism through which air is admitted to and expelled from the motor cavity. The sintered breather may also be of a sufficient thickness to be able to act as a flame arrestor for preventing a flame caused by a spark from the electric motor's commutator and / or brush from causing a fire or an explosion in the motor cavity or fuel tank. I.e. preferably the breather is of sufficient thickness to quench any flame or hot gasses developing within the motor cavity from escaping into the fuel tank. The thickness of the sintered breather may therefore for example be in the range of 2 to 2.5mm. Preferably the breather presents a mesh of 100 microns (μm) and preferably the sintered material is of grade 60 and preferably the breather has a diameter approximately 10.5mm and a thickness of approximately 2.5mm. It is also envisaged that the breather could be made of other materials. For example, the breather could be made of synthetic reverse osmosis materials which encourage flow preferentially in one direction. The fuel pump may include a fuel outlet through which fuel pumped by the pumping mechanism may exit the pump to a fuel supply circuit of a fuel injected internal combustion engine. The fuel exiting the fuel outlet may pass through a bypass regulator of the fuel supply circuit that may typically return a significant portion of the fuel back to the fuel pump. Typically, at least 50% of the fuel can be expected to be returned to the fuel pump under normal operating conditions. Under idle conditions of the engine, the fuel return may be up to about 98%. The returned fuel may be directed to a void (or a space) located above the sintered breather so as to allow the returned fuel to wet the breather. A spigot may support a fuel return line which may direct the fuel to the space above the breather. When the level of fuel in the tank falls below the level of the breather, some, or all, of the fuel from the fuel return path may be drawn through the breather and into the motor cavity, thereby falling onto the motor or the head of fuel in the cavity containing the motor. This ensures that the motor remains at least partially flooded with fuel even when the fuel level within the fuel tank drops below the level of the breather in the fuel pump. It also helps to provide lubrication to the motor as the fuel that falls onto the rotor is dispersed throughout the moving parts of the motor. Also, maintaining fuel within the motor cavity can help to maintain the air / fuel ratio within the motor cavity at a sufficiently rich level that flames are quenched within the cavity, which can assist with suppressing fire and / or explosion that may arise from the use of an electric motor. Accordingly it is also preferable that the motor is intermediate the breather and the inlet so that an additional advantage of the motor having fuel flowing through it may also be achieved. The abovenoted fuel return arrangement maintains the sintered breather in a wet condition. This leads to a particular operational advantage in that the fuel pump can almost entirely empty the fuel tank. This is because when the level of fuel in the tank falls below the level of the breather and the breather is wet, typically under the action of a fuel return line, a surface tension effect on the breather is believed to create a partial vacuum in the motor fuel pump housing resulting in fuel being drawn in through a vent or passage located on the fuel inlet side of an inlet valve and into the pump mechanism and through into the motor cavity. Accordingly the breather has been observed to assist with priming of the pump as it allows air trapped in the motor cavity to escape. And when the level of fuel in the tank falls below the level of the breather a wetted breather is believed to create a partial vacuum in the motor cavity that assists with pumping of fuel. In this sense the breather may operate to provide selective impedance to air flow through the pump housing. When the fuel pump, according to the present invention, is used in a small engine application, for example a scooter, it is preferable that the fuel pump has a small current draw, for example 0.5 Amps at 14V and preferably no greater than 0.8 Amps at 14V, while, at the same time, providing fuel at sufficient pressure for a small engine port injected fuel system or a direct fuel injection system. Accordingly it is preferable that the pump supply fuel at pressures exceeding 400Kpa (Kilo Pascal) for this level of current draw and more preferably in excess of 600Kpa. A typical dual fluid direct injection fuel system (also known as a low pressure direct injection fuel system) delivers fuel at a pressure of 750Kpa and the pump has been observed to supply fuel at this pressure with a current draw of less than 0.8 Amps and typically in the order of 0.6 Amps. The pump has also been observed supplying fuel at pressure in the order of 20 Bar. The pumping mechanism may include an elongate piston, the length of which is substantially greater than the cross-sectional diameter of the piston. The piston may be slidably accommodated within an elongate piston passage. The piston when accommodated within the piston passage defines a variable volume pump chamber which is in fluid communication with the fuel inlet and fuel outlet of the fuel pump. The piston may be actuated for reciprocal movement by means of a crank pin and slider mechanism or conrod mechanism. This mechanism may include a crank pin supported on, and extending from, a drive shaft of the motor. The crank pin may engage a slider mechanism attached to one end of the elongate piston. It is also envisaged that the piston may be actuated by means of a conrod supported at one end on the motor drive shaft and the other end on the piston. Such a drive arrangement is described in the Applicant's abovenoted International application. The above-noted drive arrangements for the piston mechanism may be located within a chamber located within the fuel pump and in communication with the cavity locating the motor. A vent line may connect this chamber with the fuel inlet to thereby allow for fluid flow into this chamber and, hence, into the motor. Where a partial vacuum is created within the motor cavity, this vent line assists with communicating fuel from the inlet valve area to the motor cavity. In this way the level of fuel in the motor cavity can be greater than the level of fuel in the tank. The fuel in the motor cavity is thereby believed to act as a secondary source of fuel for the inlet valve. A filter may be provided at the fuel inlet to filter the fuel entering the fuel pump from the fuel tank. The filter preferably has a mesh less than 100 /m, and preferably of a size comparable with any filter employed within a fuel injector of a fuel system supplied by the pump. A fuel pump according to the present invention is therefore particularly adapted for use within a fuel tank, with the electric motor being readily flooded with fuel to thereby prevent the generation of sparks between the commutator and brush. Furthermore, the breather arrangement also acts as a flame arrester if any such sparks are generated. The fuel pump also has the ability to substantially fully empty the fuel pump thereby helping to maximise the potential driving range of the vehicle in which the fuel pump is installed. According to a further aspect of the present invention there is provided a fuel pump of a fuel circuit for an internal combustion engine; said fuel pump adapted for location in a fuel tank, said fuel circuit having an auxiliary fuel path and said fuel pump further adapted to receive said auxiliary path whereby in use a motor of said fuel pump is located in said auxiliary path. Alternatively, this aspect provides a fuel circuit for an internal combustion engine comprising a fuel pump and an auxiliary fuel path; said fuel pump adapted to receive said auxiliary fuel path whereby in use a motor of said pump is located in said auxiliary path. Preferably said auxiliary fuel path is a fuel return circuit for in use returning excess fuel to said fuel tank. Preferably said pump comprises a filter intermediate said auxiliary path and said motor. Preferably said filter is a breather and preferably said motor is located in a motor cavity and said breather provides impedance to air flow into said motor cavity whereby in use said breather creates a partial vacuum in said motor cavity. Preferably said breather provides said impedance in use when wetted by fuel from said auxiliary path and preferably said breather provides minimal impedance when dry. Preferably said impedance is sufficient to create a partial vacuum capable of lifting fuel from an inlet filter to at least an inlet valve and more preferably to a motor cavity via a vent line communicating an area adjacent the inlet valve with the motor cavity. The applicant has found that when the breather is dry, fuel can be lifted through a height of 20 - 25 mm when the pump operates in the range of 8V to 14V terminal voltage and when the breather is wet the fuel can be lifted through a height of 55 - 65 mm for terminal voltage in the range of 8V - 14V. Hence a wet breather has been observed to increase the height through which fuel can be lifted by 35 - 40 mm when a breather having a mesh size of 100μm was used. According to a further aspect of the present invention there is provided a fuel pump for an internal combustion engine, said pump comprising a fuel inlet located at a level below a breather in said pump; said breather providing impedance to air flow through said pump thereby creating at least a partial vacuum in said pump; said partial vacuum in cooperative association with said inlet so as to assist with drawing fuel through said fuel inlet. Preferably said breather is operatively located in association with a first cavity separate from an outlet side of said inlet valve; said first cavity in fluid communication with an area adjacent the inlet side of said inlet valve. Preferably said first cavity is a housing for a motor for said pump and a vent line provides fluid communication between said housing and said area adjacent the inlet side of said inlet valve. According to a further aspect of the present invention there is provided a fuel circuit for at least a dual fluid fuel injection system wherein fuel supplied by said fuel circuit comprises a first of said fluids and a propellant fluid comprises a second of said fluids; said fuel circuit comprising a fuel pump adapted to provided fuel under pressure and at intermittent pulses and a pressure regulator for supplying said fuel to a fuel metering device; said pressure regulator operating at a differential pressure that is differential to the fuel pressure and the pressure of said second fluid; said differential pressure being less than said pressure pulses whereby metering of said fuel by said fuel metering device is precise to within predetermined tolerances. Preferably said fuel pump is a single chamber pump. Preferably said pressure differential is less than one quarter of said pressure pulse and more preferably it is less than one fifth of said pressure pulse. Preferably said second fluid is air that is supplied at approximately 500 Kpa and said fuel is supplied at approximately 750Kpa and said pump has a displacement of 0.041 CC (cubic centimeters) per stroke and said fuel circuit supplies fuel to a 50CC engine. Preferably said pump has a DC motor that draws current in the range of 600mA to 200mA at terminal voltage varying between 14V and 7V. However at 12V it is also preferred that the pump draws approximately 450mA. At 14V the DC motor preferably operates at approximately 3900 RPM (revs per minute) and at 12V approximately 3300 to 3400 RPM. The pump may operate outside these specified ranges, however the specified ranges are preferred operational parameters. In particular it has been observed that such a 0.041 CC per stroke pump typically draws less than 8.4 Watts electrical power when delivering fuel at 750KPa which translates into between 16 Watts and 30 Watts mechanical power. A typical 50CC engine develops approximately 3.75KW and therefore the pumps represents less than a 1 % parasitic to the mechanical power developed by the engine. It will be convenient to further describe the invention with respect to the accompanying drawings which illustrate at least one possible embodiment. Other embodiments of the invention are possible and, consequently, the particularity of the accompanying drawings and description is not to be understood as superseding the generality of the preceding description of the invention. In the drawings: Figure 1 is a representative fuel injected small engine scooter. Figure 2a and 2b are schematic representations of fuel injected engines and associated fuel supply circuits suitable for use in the scooter of Figure 1 and other small engine applications. Figure 3 is a perspective view of a fuel pump of the type employed in the fuel circuit of Figures 2a and 2b; Figure 4 is a cross-sectional view of the fuel pump of Figure 3. The present embodiments are particularly suited to application as "in- tank" fuel pumps for small engine vehicles such as motorscooters, that utilise port injected fuel systems, low pressure direct injection fuel systems and other direct injection fuel systems for internal combustion engines. Examples of a low pressure dual fluid direct injection fuel system for an internal combustion engine is detailed in the applicants patents US 4,693,224; & US 4,934,329 incorporated herein by reference. Small engine vehicles and other applications typically have capacity in the order of 50cc to 100cc and they typically have low battery capacity and so a low current motor for the pump, in the order of 0.5 amps is particularly suitable. The embodiments also have application in fuel circuits that pump fuel from a fuel source such as a fuel tank to an internal combustion engine and then circulate excess fuel back to the fuel source. To better understand the environments within which the embodiments are employed, Figure 1 , which is a schematic illustration of a scooter 300 being a representative small engine application for an in-tank pump, will now be described. The scooter has a front wheel 305 and a rear wheel 310 which support a chassis and associated panel work 315 off of a road surface 320. The chassis and panel work 315 comprises a rider area 325 which typically consists of a seat that is capable of supporting two riders. The rider area 325 is located above the rear wheel 310. An engine and associated drive mechanism 330 is mounted intermediate the rider area 325 and the rear wheel 310. Handle bars 335 are rotationally mounted to the chassis and panel work 315 and further support shock absorbers 340 that located the front wheel 305 onto the scooter 300. In operation a rider positions themselves onto the rider area and locate their feet on foot rests 345 located on a floor pan 350 of the chassis and associated panel work 315. These foot rests 345 are located intermediate the base of handle bars 335 and the rider area 325. The handle bars 335 contain a mechanical throttle actuation mechanism which may be actuated by the rider rotating their hand. The handle bars 335 also contain an ignition switch which activates an electrical circuit between a battery, located adjacent the engine and associated drive mechanism 330, and an electronic control unit and other electrical components, such as a fuel pump and headlights 355. The scooter has a single cylinder fuel injected engine with small capacity which may be in the range of 50CC to 100CC though utilisation of an increased capacity engine is also possible. A fuel tank supporting an in-tank pump may be located underneath the riders area 325. The in-tank pump supplies fuel to a fuel supply circuit that is in communication with a fuel injector of the engine. Referring now to Figure 2a and 2b each of which is a schematic representation of an engine and an associate fuel supply circuit suitable for use with the scooter of Figure 1 and other fuel injected applications and in particular small engine applications. The engine and associated fuel system of Figure 2a is a direct injected single cylinder two stroke engine 50 having a fuel tank 1 which communicates fuel to a fuel injector 5 by means of a fuel pump 3 located within fuel tank 1 as described in this specification. The fuel supply circuit also includes fuel pressure regulator 4 and fuel supply line 52 and fuel return line 53. The fuel injector 6 meters fuel to a fuel delivery injector 7 in accordance with metering signals received from engine control unit (ECU) 11. The fuel delivery injector 7 is in fluid communication with compressed air via air supply line 70 that receives compressed air from air compressor 13. The compressor 13 is driven by a roller follower that is activated by an eccentric cam 68 that is mounted to or that forms part of a flywheel 67. The fuel delivery injector 7 uses compressed air as a propellant to deliver fuel metered by the fuel injector 5 to combustion chamber 61 of engine 50. Further examples of fuel systems of this type may be found in the Applicant's United States Patents US 4,693, 224 and US 4,934,329 referred to previously. The fuel delivery injector 7 delivers a spray of fuel to the combustion chamber 61 in a manner so that the fuel passes across a spark gap of spark plug 8. The spark plug is controlled by ignition coil 10 which in turn is activated by ECU 11. Under certain engine operating conditions, which are typically low to medium load and low to medium speed conditions, the engine 50 operates by establishing a stratified charge of fuel in the combustion chamber which is ignited by spark plug 8. Preferably the spark plug ignites the fuel spray as it issues from the fuel delivery injector 7 so as to provide a spray guided combustion system. Airflow is provided to the combustion chamber 61 via air box 18 and air filter 19. The air box 18 is in fluid communication with an inlet manifold 65 intermediate throttle 16 and inlet reed valve 64. A combined manifold absolute pressure (MAP) sensor and temperature sensor 20 often referred to as a TMAP sensor is located in the inlet manifold. The TMAP sensor provides MAP signals to ECU 11 that indicate pressure in the inlet manifold 65 and that similarly provides temperature signals to the ECU 11 that indicate the temperature of air entering the engine 50. The TMAP sensor 20 is an analogue sensor whose signals may be sampled by ECU 11 through use of analogue to digital conversion techniques and digital sampling filtering techniques. Air flow to the engine is in part controlled by the position of throttle 16. This position is indicated to ECU 11 by throttle position sensor 15. Oil is supplied to the engine 50 by oil pump 17 which is controlled by ECU 11 and which receives oil from oil tank 12. Electrical power is supplied to the engine (including the fuel pump), at least at cranking, by battery 22 and ignition switch 21. The ECU 11 receives information as to the position of piston 60 within the combustion chamber 61 by crank shaft position sensor 14 and an encoder wheel 66 mounted on fly wheel 67. Encoder wheel 66 comprises a number of teeth, typically 24 (one of which may be missing so as to provide a reference tooth) which pass by position sensor 14. The teeth interact with position sensor 14 so as to generate a square wave signal as input to ECU 11. the square wave is commonly edge detected by the ECU 11 resulting in detection of each leading edge of the encoder wheel 66 as it passes position sensor 16. The information as to the position of the piston 60 within combustion chamber 61 is commonly referred to as the engine's crank angle. A two stroke engine cycle is said to have 360 s of crank angle whereas a four stroke engine cycle is said to have 720 s of crank angle. Thus in operation an engine's crank angle corresponds to the instantaneous position of the engine within its current engine cycle. This position is measured relative to the engines top dead center (TDC) position, which for a two stroke engine is the point of maximum compression on any engine revolution and for a four stroke engine is the point of maximum compression on an intake (i.e. compression) stroke and which is often referred to as TDC firing. A 24 tooth encoder provides 15 Q of crank angle resolution for both a two stroke and a four stroke engine. Figure 2b is a schematic representation of a single cylinder four stroke port injected engine 150 similar to the two stroke engine 50 of Figure 4a. The four stroke engine 150 has a fuel tank 101 that communicates fuel to a fuel injector 111 under control of an ECU 116 via a fuel filter 102, an in tank fuel pump 103, and a fuel pressure regulator 104. A fuel pressure regulator 174 is formed integrally with the pump 103, or if not integrally with the pump at the point where the pump is mounted to the fuel tank 101. Accordingly, a single fuel supply line 172 extends from regulator 174 to fuel injector 172. A fuel return path 173 extends from the regulator 174 to the pump 103. Air is inlet to the combustion chamber 161 via air box 105 that houses air filter 106 and inlet manifold 165 that houses a throttle 109, a TMAP sensor 107, a throttle air bypass valve 108 and fuel injector 111. An air inlet valve 151 is actuated under operation of a cam (not shown) so as to communicate air in the inlet manifold with the combustion chamber. Fuel injector 111 sprays fuel into the inlet manifold which fuel is then transported into the combustion chamber 161 by the inlet air so that a homogenous charge of fuel is formed within combustion chamber 161. Spark plug 112 operates under the control of ignition coil 113 which is in turn controlled by ECU 116. An exhaust valve 152 is actuated under operation of a cam to permit egress of combustion gasses from the combustion chamber on an exhaust stroke. An engine temperature sensor 114 indicates engine temperature to the ECU 116. The engine 150 has an engine position sensor 115 and corresponding encoder wheel for indicating the engine's instantaneous crank angle when operational. The engine 150 (including fuel pump 103) is supplied electrical power, . at least at cranking, by means of a battery 118 and an ignition switch 117. Referring to Figures 3 and 4, which provide further detail on a fuel pump suitable of location within a fuel tank, such as the fuel tank 101 and the fuel tank 1 detailed above, according to one preferred embodiment. The fuel pump includes a fuel pump housing 1 within which is located an electric motor 3 and pump arrangement 5. Located at one end of the fuel pump housing 1 is an intake filter 7 for filtering fuel entering the fuel inlet 9 of the fuel pump. When the fuel pump is located within a fuel tank, the filter 7 is located at or near the bottom of the fuel tank and may be located within a depression in the bottom of the fuel tank. Fuel passing through the filter 7 into the fuel inlet 9 passes through an inlet valve assembly 11. This inlet valve assembly 11 is described in detail in the Applicant's International Application No. PCT/AU99/00601 and will therefore not be described herein in any detail, however it should be noted that this arrangement does provide a pump that is efficient at high pressure, which allows for lower levels of current to be drawn by the pump motor compared with less efficient pumps of similar capacity (which capacity is in the order of 0.04 CC per stroke). A further feature of the pump is that it can be arranged to displace lower volumes of fuel at high pressures suitable for small engine fuel injection applications. By displacing lower volumes of fuel compared with typical fuel pumps (along with being relatively efficient), the pump has a lower current draw, which is advantageous for small engine applications where the parasitic losses to engine power of a high current fuel pump can be significant. The configuration of the pump arrangement 5 means that the output of the pump has a pulsating or intermittent characteristic. Further detail on the effect of this intermittent characteristic is provided herein. The intake filter 7 may be of a woven fabric such as a woven nylon, polyester or other suitable plastics and / or fabrics well known in the art and preferably has a mesh size less than 100μm, although a smaller mesh size comparable to any mesh utilised as a filter in a fuel injector supplied with fuel by the fuel pump may also be used. Preferably the intake filter is of a type having an inlet tube extending to the base of the filter. The inlet tube has apertures adjacent the base of the filter so that fuel is drawn by the inlet valve assembly from adjacent the base of the filter. In operation fuel passes from the inlet valve assembly 11 into a pump chamber 13 of the pumping arrangement 5. The pumping arrangement 5 includes an elongate piston 15 located within a piston passage 17 which together define the variable volume pump chamber 13. The piston 15 is driven for reciprocal movement by a drive arrangement 19 which includes a crank pin 21 supported on, and extending from, a drive shaft 6 of the electric motor 3. The crank pin 21 co-operates with a one end of a conrod mechanism 23 which is supported at the other end by the piston 15. Preferably the conrod, its supporting structure and engagement mechanism with crank pin 21 (such as an eyelet) are constructed from a self lubricating plastic suitable for high pressure velocity applications such as Polyetheretherketone (PEEK) as described in the Society of Automotive Engineers (SAE) paper 970244 "Lubriacted Thermoplastic Composites for High P-V Applications" Williams, E.H. Other materials such as PPS(OBG) and PPA(BQU) which are also described in SAE 970244 Williams, E. H. may form suitable alternatives. The drive arrangement 19 is supported within a chamber 25 located under and open to the electric motor 3. An internal vent line 27 communicates this chamber 25 with the fuel inlet 9 at a location on the inlet side of fuel inlet valve assembly 11. Preferably the vent line 27 and the inlet side of the fuel inlet valve assembly 11 have a proximity such that the fuel inlet valve assembly 11 can draw fuel from or access fuel supplied from chamber 25 via vent line 27. Fuel pumped from the pumping chamber 13 passes through a fuel outlet valve 29 and through a fuel outlet passage 31 to a fuel outlet 33 of the fuel pump. In the embodiments, the fuel inlet is at a level below the fuel outlet. This is advantageous in certain "in tank" applications, though it is not believed to be essential to the operation of the embodiment. A pressure relief valve 50 communicates fuel from the outlet passage 31 to chamber 25 when pressure within the outlet passage 31 exceeds a pre-determined minimum value. The relief valve 50 operates according to principles known in the art and accordingly is not further described. The electric motor 3 is supported within a motor cavity 10 in the fuel pump housing 1. This cavity 10 is closed off at the top thereof by an end cap 12. Supported within the end cap 12 is a sintered breather 2. This sintered breather 2 is positioned adjacent an aperture 8 passing through the end cap 12. The breather allows air to flow from the motor cavity to a point external of the pump. When the fuel pump is located within a fuel tank, the fuel pump can be totally submerged within the fuel. In these situations, fuel can pass through the fuel inlet 9, through the inner vent line 27 into the cavity 25 and hence through the motor cavity 10. The fuel passes or percolates through the electric motor 3 and any air or fuel vapour within that motor cavity 10 passes out through the sintered breather 2 and the aperture 8 out of the fuel pump. This allows fuel to rise within the motor cavity 10 to the level of the fuel in the tank which in turn allows the motor 3 to be flooded when the pump is submerged, or at least partially submerged, by fuel within a fuel tank. This flooding of the motor with fuel assists with preventing sparks being generated between the electric motor's commutator and brush (not shown). Flooding of the motor and the motor cavity means that in operation fuel is drawn by the inlet 9 and the variable volume chamber 13 from both the filter 7 and the motor cavity 10 via vent line 27. The primary draw however is believed to be through the inlet filter 7. During operation of certain fuel circuits a significant portion of fuel pumped through a fuel pump is returned to a fuel source such as a fuel tank. Typically, at least 50% of the fuel is returned during operation of the engine and at idle up to 98% of the fuel may be returned. According to one embodiment, the fuel delivered from the fuel pump to a fuel circuit passes through a by-pass regulator (not shown) which ensures that fuel that is not delivered to the engine by the fuel circuit is returned via a return line to the fuel source. In preferred embodiments the return line is connected to a fuel return spigot 35 of the fuel pump. This allows returned fuel to enter a volume 37 above the sintered breather 2. This ensures that the breather 2 remains wetted with fuel when the fuel level in a fuel tank housing the pump drops below the level of the sintered breather 2. It has been found that if the sintered breather 2 is wet, and the level of fuel in the tank drops below the level of the sintered breather, a resultant surface tension effect within the breather creates a partial vacuum in the fuel pump housing 1. This results in fuel being drawn in through the fuel inlet 9 into the cavity 25 via vent line 27 which has been observed to maintain fuel in the motor cavity 25 at a level above the level of fuel in the tank. It is believed that this increase in negative head pressure assists the fuel pump to continue pumping fuel even when the fuel level drops below the level of the inlet valve 11. Indeed, it has been found that the fuel pump will continue to pump until the fuel level drops to near the bottom of the pick up 41 of the filter 7. The fuel pump according to the present embodiment can therefore almost entirely empty the fuel tank. Alternatively a breather that provides impedance to air flow is believed to also provide such a partial vacuum. Such a partial vacuum is also achieved due to the provision of a pump housing that is sealed apart from the breather and the inlet 9. It is also believed that some, if not all of the fuel, that returns along the fuel return path, may pass through the breather and onto the motor in the motor cavity. This helps to keep the motor wetted with fuel. The fuel is believed to act as a lubricant for the motor and hence this return path of fuel through the motor is believed to be particularly advantageous where the level of fuel in the tank is such that the motor is no longer flooded. A further advantage of the return path through the motor cavity is that additional fuel in the motor cavity assists with lowering the air / fuel ratio within the cavity 10 to below a stoichiometric ratio which can assist with quenching any flame that may develop within the cavity. In this regard, any flame that may arise within the motor chamber is believed to be quenched by use of a breather of sufficient thickness to prevent the flame escaping into the fuel tank generally and causing an explosion and to prevent hot gasses re-igniting once they have passed through the breather. The breather may be constructed of sintered metal. A thickness of between 2mm and 2.5mm is believed to be effective, however 2.3mm has been found to be sufficient for a small engine application fuel pump. A breather having a diameter of approximately 10.5mm and a thickness of approximately 2.5mm and that is constructed from grade 60 sintered material so as to present a mesh of approximately 100μm has been found to be particularly effective, however a breather presenting a mesh in the range of 80μm to 120μm is also believed to be effective. It is also believed that other materials providing impedance to air flow may also provide effective alternatives to the sintered breather material detailed. For example metal woven mesh or alternate forms of flame arrestors may also be suitable. Alternate embodiments may not have a fuel return circuit or may not locate the fuel return path adjacent an aperture into a cavity housing the motor. In these embodiments an additional fuel path, such as a branch line from a main supply line or a return line, that feeds fuel to the breather so as to maintain the breather in a wetted state or so as to maintain fuel flow over the motor is envisaged. Whilst it is often not necessary to provide a breather in a fuel circuit that returns fuel through an in-tank motor, in some applications it is preferable that such a circuit have such a breather or filter. Alternatively, it believed that acceptable operation may be derived from a pump having a breather and a fuel return circuit that bypasses the breather. As detailed above, the in-tank fuel pump mechanism of figures 4a and 4b is a single chamber arrangement that provides higher efficiency (in the order of 30%) at higher pressures and lower flow rates than standard fuel pumps (that are in the order of 15% efficient). This enables the pump to draw less than 800mA and typically 500mA when used in a small engine application, such as a motorscooter. In achieving this low current draw the pump has an intermittent output, that is seen as pressure pulses of fuel within the fuel supply circuit. In a dual fluid fuel injection system of a type referred to above, fuel is typically metered to an air assisted delivery injector via a fuel injector commonly used in port injected systems. To accurately meter fuel, the fuel injector needs to see a relatively stable fuel pressure at its fuel inlet. In a dual fluid system, it is common for the fuel pressure seen by the fuel injector inlet to be set relative to the pressure of the second fluid, typically compressed air. Typically the delivery injector is in continuous communication with a pressurised source of the second fluid. Accordingly, the fuel supply circuit typically has a higher pressure than the second fluid so that it can be metered into the delivery injector against the pressure of the second fluid. A differential pressure control regulator is typically used to achieve this differential pressure between the fuel supply pressure and the pressure of the second fluid. Where the fuel supply circuit sees pressure pulses due to the use, for example, of a single chamber reciprocating fuel pump mechanism, it is preferable that the pressure differential between the fuel supply pressure and the pressure of the second fluid be exceeded by the level of the pressure pulses by an amount such that a generally constant pressure is seen at the inlet to the fuel injector that meters fuel into the fuel delivery injector. This generally constant pressure should be sufficient to allow metering of fuel into the fuel delivery injector within predetermined metering tolerances. For example, in the 50CC scooter engine of Figure 2a a pump of the embodiments above having a 4mm diameter plunger that delivers 0.041 CC per stroke, at a pressure differential of 250Kpa between fuel pressure and compressed air was found to be sufficient. To this end, fuel pressure was approximately 750Kpa and the pressure of the compressed air was approximately 500Kpa. The pump operated off of a DC motor with a frequency of 3900 strokes per minute with a 14V supply across the terminals and at 12V the pump typically operates between 3300 and 3400 strokes per minute. Accordingly a typical pump in production can be expected to draw less than approximately 11.2 watts of electrical power (i.e. less than 0.8Amps at 14V), which typically represents between 20 and 30 watts of mechanical power depending on the efficiency of the alternator or magneto driving the electric motor of the pump. A typical 50CC engine generates power in the order of 3.75 KW and accordingly a typical production pump is likely to represent less than a 1% parasitic to mechanical power of the engine. Plungers having a diameter greater than 4mm are possible. The following details have been observed for various pumps delivering fuel at 750Kpa with a 14V across the motor terminals: It has also been observed that a representative pump with a 4mm plunger can develop up to 20 Bar pressure in a fuel line. It has also been observed that a pump having a 4mm plunger and a breather with a diameter of approximately 10.5mm, a thickness of approximately 2.5mm and presenting a mesh of approximately 100μm was capable of lifting fuel through a negative suction head of between 20 and 25mm for terminal voltage in the range 8 - 14 Volts with a dry breather. It has also been observed that with a wet breather, as provided by locating the breather in a fuel return path, the negative suction head range increased to 55 - 65 mm for the same terminal voltages. This increased negative suction head is believed to arise as a result of a partial vacuum within the motor cavity created by surface tension effects when the breather is wet and when the fuel level in the tank is below the level of breather. The increased negative suction head is also believed to draw fuel along vent line 27 and into the motor cavity resulting in the level of fuel in the motor cavity often exceeding the level of fuel in the tank. It is believed that this negative suction head allows the pump to almost fully empty a fuel tank (i.e. allows the pump to draw fuel from below the level of the inlet valve assembly 11). Present embodiments provide a fuel pump that may be located within a fuel tank and submersed in fuel. The fuel pump provides fuel at sufficient pressure for a direct injection fuel system and at sufficiently low power consumption that it can be utilised in small engine applications. Alterations and variations to the invention and embodiments as described herein are included within the ambit of the claims appended hereto.

Claims: In the Claims: 1. A fuel pump locatable within a fuel tank including: a fuel pump housing; a pumping mechanism located within the housing for pumping fuel; an electric motor for driving the pumping mechanism, the motor being accommodated within a motor cavity with the housing; a fuel inlet for the pumping arrangement; wherein the fuel pump housing includes a breather arrangement for allowing air and fuel vapour within the cavity to escape therefrom when displaced by fuel passing into the motor cavity. 2. A fuel pump according to claim 1 , wherein the breather is further adapted to operate as a filter. 3. A fuel pump according to claim 1 or 2, wherein the breather provides impedance to air flow into and out of the motor cavity after priming of the pump. 4. A fuel pump according to any one of claims 1 to 3, wherein the fuel inlet is positioned below the breather when the pump located for use within a fuel tank, so that the breather can assist with priming the pump. 5. A fuel pump according to any one of the preceding claims, wherein the breather arrangement is in the form of a sintered breather plate or disc. 6. A fuel pump according to claim 5, wherein sintered breather is located above the motor adjacent an aperture in the fuel pump housing or in an end cap separable from the rest of the housing when the fuel pump is in its in use position. 7. A fuel pump according to claim 5 or 6, wherein the sintered breather is of a sufficient thickness to be able to act as a flame arrestor for the electric motor. 8. A fuel pump according to any one of claims 5 to 7, wherein the sintered breather is dry during the priming of the pump to thereby allow the escape of trapped air from the pump, and is maintained in a wetted state during operation of the pump to assist in providing a partial vacuum therein. 9. A fuel pump according to any one of claims 1 to 4, wherein the breather arrangement is in the form of a plate or disc made of a synthetic reverse osmosis material which encourages preferential flow in one direction. 10. A fuel pump according to any one of the preceding claims, wherein the pump includes a fuel outlet through which fuel pumped by the pumping mechanism may exit, wherein the fuel exiting the fuel outlet pass through a bypass regulator for returning a significant portion of the fuel back to the fuel pump. 11. A fuel pump according to claim 10, wherein at least 50% of the fuel is returned to the fuel pump under normal operating conditions, and wherein up to about 98% of the fuel is returned under idle conditions of the engine. 12. A fuel pump according to claim 10 or 11 , wherein the returned fuel is directed to a space located above the breather arrangement such that the electric motor remains at least partially flooded with fuel when the fuel level falls below the level of the breather arrangement. 13. A fuel pump according to claim 12, wherein the motor is located intermediate the breather arrangement and the inlet to facilitate a fuel flow through the motor during operation of the pump. 14. A fuel pump according to any one of the preceding claims, wherein the pumping mechanism includes an elongate piston, the length of which is substantially greater than the cross-sectional diameter of the piston, the piston being slidably accommodated within an elongate piston passage to thereby define a variable volume pump chamber which is in fluid communication with the fuel inlet and fuel outlet of the fuel pump. 15. A fuel pump according to claim 14, wherein the piston is actuated for reciprocal movement by a drive arrangement including a crank pin and slider mechanism including a crank pin supported on, and extending from, a drive shaft of the motor, the crank pin engaging a slider mechanism attached to one end of the elongate piston. 16. A fuel pump according to claim 14, wherein the piston is actuated for reciprocal movement by a drive arrangement including a cam supported on the motor drive shaft and abutting a cam follower located at said end of the piston. 17. A fuel pump according to claim 15 or 16, wherein the drive arrangement is located within a chamber located in the pump under the motor. 18. A fuel pump according to claim 17, wherein a vent line connects the chamber with the fuel inlet to thereby allow for fluid flow into the chamber, and hence into the motor. 19. A fuel pump of a fuel circuit for an internal combustion engine; said fuel pump being adapted for location in a fuel tank, said fuel circuit having an auxiliary fuel path and said fuel pump further adapted to receive said auxiliary path whereby in use a motor of said fuel pump is located in said auxiliary path. 20. A fuel pump according to claim 19, said auxiliary fuel path being a fuel return circuit for in use returning excess fuel to said fuel tank. 21. A fuel pump according to claim 19 or 20, wherein said pump includes a filter intermediate said auxiliary path and said motor. 22. A fuel pump according to claim 21 , wherein said filter is a breather and said motor is located in a motor cavity , said breather providing impedance to air flow into said motor cavity whereby in use said breather creates a partial vacuum in said motor cavity. 23. A fuel pump according to claim 22, wherein said breather provides said impedance in use when wetted by fuel from said auxiliary path and said breather provides minimal impedance when dry. 24. A fuel pump according to claim 23, wherein said impedance is sufficient to create a partial vacuum capable of lifting fuel from an inlet filter to an inlet valve. 25. A fuel pump according claim 24, wherein the partial vacuum is capable of lifting fuel to a height of about 30mm. 26. A fuel circuit for an internal combustion engine including a fuel pump and an auxiliary fuel path; said fuel pump being adapted to receive said auxiliary fuel path whereby in use a motor of said pump is located in said auxiliary path. 27. A fuel pump for an internal combustion engine, said pump including a fuel inlet located at a level below a breather in said pump; said breather providing impedance to air flow through said pump thereby creating at least a partial vacuum in said pump; said partial vacuum in cooperative association with said inlet so as to assist with drawing fuel through said fuel inlet. 28. A fuel circuit for at least a dual fluid fuel injection system wherein fuel supplied by said fuel circuit comprises a first of said fluids and a propellant fluid comprises a second of said fluids; said fuel circuit comprising a fuel pump adapted to provided fuel under pressure and at intermittent pulses and a pressure regulator for supplying said fuel to a fuel metering device; said pressure regulator operating at a differential pressure that is differential to the fuel pressure and the pressure of said second fluid; said differential pressure being greater than said pressure pulses whereby metering of said fuel by said fuel metering device is precise to within predetermined tolerances. 29. A fuel circuit according to claim 28, wherein the fuel pump is a single chamber pump. 30. A fuel circuit according to claim 28 or 29, wherein said pressure pulse is less than one quarter of said pressure differential, preferably less than one fifth of said pressure differential. 31. A fuel circuit according to any one of claims 28 to 30, wherein said second fluid is air supplied at approximately 500 Kpa, said fuel is supplied at 750Kpa, said pump has a displacement of 0.041 CC per stroke and said fuel circuit supplies fuel to a 50CC engine. 32. A fuel circuit according to claim 31 , wherein said pump has a DC motor that draws current in the range of 600mA to 200mA at terminal voltage varying between 14V and 7V 33. A fuel circuit according to claim 32, wherein the pump draws approximately 450mA at 12V 34. A fuel circuit according to claim 32 or 33, wherein at 14V the DC motor operates at approximately 3900 RPM, and at 12V approximately 3300 to 3400 RPM. 35. A scooter having an internal combustion engine with at least one fuel injector receiving fuel from a fuel supply circuit including a fuel pump located within a fuel tank, the fuel pump developing less than 1% parasitic loss of mechanical power developed by said engine. 36. A scooter as claimed in claim 35 wherein said fuel injector is a direct injection fuel injector receiving fuel at a pressure above 600 Kpa. 37. A scooter as claimed in any one of claim 35 or 36 wherein said engine has capacity of approximately 100CC or less. 38. A scooter having a fuel pump as claimed in any one of claims 35 to 37 wherein said pump having a pumping mechanism wherein said pump is further arranged to develop a negative suction head of at least 55mm for a pumping arrangement having a piston of approximately 4mm diameter at a fuel delivery pressure of approximately 750Kpa. 39. A scooter as claimed in claim 38 wherein said negative suction head is developed at least when the fuel in the tank has fallen to a level below the breather and wherein said breather is maintained in a wetted state by a fuel return path. 40. A scooter as claimed in any one of claims 35 to 39 wherein the fuel pump further comprises a pumping mechanism for ingress of fuel through a fuel inlet valve and egress of fuel through a fuel outlet valve, the fuel pumping mechanism driven by an electric motor located within a motor cavity, the motor cavity having a breather mechanism for drawing fuel into the motor cavity from the tank or a fuel return line. 41. A scooter as claimed in claim 40 wherein said motor cavity is in fluid communication with a point in close proximity to the inlet side of said inlet valve.

Inventors: KEELING ANTHONY DENHAM, O'BRIEN RICHARD JOHN, O'KEEFE WALTER JOSEPH, SHAMS ANDREW MASSOUD, KEELING, ANTHONY, DENHAM, O'BRIEN, RICHARD, JOHN, O'KEEFE, WALTER, JOSEPH, SHAMS, ANDREW, MASSOUD
Applicants: BRIEN RICHARD JOHN O, KEEFE WALTER JOSEPH O, KEELING ANTHONY DENHAM, ORBITAL ENG PTY, SHAMS ANDREW MASSOUD, KEELING, ANTHONY, DENHAM, O'BRIEN, RICHARD, JOHN, O'KEEFE, WALTER, JOSEPH, ORBITAL ENGINE COMPANY (AUSTRALIA) PTY LIMITED, SHAMS, ANDREW, MASSOUD
Application year: 2001
Main classification: F02M37
IPC codes: F02M37, F02M67