Field of the Invention

This invention relates to gaseous fuel injection for internal combustions engines.

The term "gaseous fuels" as used herein refers to compressed gas fuels such as compressed natural gas (CNG) and hydrogen (H ₂ ), and liquefied gaseous fuels such as liquefied petroleum gas (LPG) and liquefied natural gas (LNG).

The term "direct injection" refers to delivery of fuel directly into the combustion chambers of internal combustion engines, typically by way of fuel injectors.

Background Art

The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

Gaseous fuels are known to have certain advantages over liquid fuels (such as petrol and diesel) for internal combustion engines, particularly in relation to cost and exhaust emissions. Because of these advantages there is an increasing trend to use such fuels in engines.

One example of such use is in relation to a two-stroke direct injection gaseous fuel engine for vehicles. Typically, the vehicle is fitted with a primary fuel tank for gaseous fuel and a reserve fuel tank, the arrangement being that the fuel supply can be switched from the primary fuel tank to the reserve fuel tank when the primary fuel tank depletes to an almost empty condition. There is a need however to detect when it is imminent that there is no longer adequate gaseous fuel available in the primary tank to continue to operate the engine satisfactorily. While this could possibly be achieved through use of a fuel level sensor in the fuel tank, it is not necessarily a cost-effective solution for certain applications.

It is against this background, and the problems and difficulties associated therewith, that this invention was developed. Disclosure of the Invention

According to a first aspect of the invention there is provided a method of controlling a gaseous fuel injection system for an engine, the method comprising monitoring the supply pressure of the gaseous fuel from a source, monitoring the delivery pressure of the gaseous fuel to a fuel injector, operating the fuel injector as a function of the delivery pressure to compensate for any reduction in the delivery pressure, and detecting if a variation in the supply pressure or the delivery pressure reduces at a rate greater than a prescribed rate.

With this arrangement, the quantity of gaseous fuel delivered is a function of the duration of operation of the fuel injector.

Preferably, the operation of the fuel injector is controlled by a control means such as an electronic control unit (ECU). Specifically, the ECU determines the parameters by which the fuel injector operates. The operating parameters may, for example, comprise the duration of opening of the fuel injector, the time at which the fuel injector begins to open relative to the engine operating cycle, the time at which the fuel injector begins to close relative to the engine operating cycle, or any combination thereof.

Preferably, the ECU monitors the supply pressure and the delivery pressure of the gaseous fuel.

Preferably, the ECU refers to a "look-up" map or table to determine the required operating parameters of the fuel injector.

Preferably, in circumstances where the ECU identifies a variation in the supply pressure or the delivery pressure involving a reduction at a rate greater than a prescribed rate, the delivery of the gaseous fuel to the fuel injector is terminated.

Typically, the ECU would switch the engine to a reserve fuel supply. The reserve fuel supply may be a gaseous fuel supply or another form of fuel including a liquid fuel (such as gasoline or diesel fuel).

Preferably, in circumstances where the ECU identifies a variation in the supply pressure or the delivery pressure involving a reduction at a rate greater than a prescribed rate, a signal is emitted indicating that the source is running out of gaseous fuel. The signal emitted by the ECU may initiate a switch to the reserve fuel supply.

In effect, the ECU recognises a change in the operating characteristics of the fuel injection system while the engine is operating and initiates action in response thereto, which may involve switching the fuel supply to the reserve supply.

Accordingly, the invention seeks to use the decaying pressure characteristic of a depleting gaseous fuel source (which is typically an emptying gas vessel) while the engine is operating to recognise that event and initiate subsequent action. The subsequent action may take any appropriate form, such as emitting a signal indicating that the gaseous fuel source has depleted to a predetermined extent and/or switching engine operation to the reserve fuel supply, thereby avoiding poor engine performance due to excessively low gas pressure.

According to a second aspect of the invention there is provided a gaseous fuel injection system for an engine, the fuel injection system comprising means for monitoring the supply pressure of the gaseous fuel from a source, means for monitoring the delivery pressure of the gaseous fuel to a fuel injector, and means for operating the fuel injector as a function of the delivery pressure to compensate for any reduction in the delivery pressure and detecting a reduction in the supply pressure or the delivery pressure at a rate greater than a prescribed rate.

According to a third aspect of the present invention there is provided an engine having a fuel injection system comprising a first fuel supply for a gaseous fuel, a second fuel supply, means for monitoring the supply pressure of the gaseous fuel from the first fuel supply, means for monitoring the delivery pressure of the gaseous fuel to a fuel injector, and means for operating the fuel injector as a function of the delivery pressure to compensate for any reduction in the delivery pressure and detecting a reduction in the supply pressure or the delivery pressure at a rate greater than a prescribed rate, and means for switching the engine from the first fuel supply to the second fuel supply upon detection of a reduction in the supply pressure or the delivery pressure of the gaseous fuel at a rate greater than a prescribed rate.

According to a fourth aspect of the invention there is provided a vehicle having an engine according to the third aspect of the invention. Brief Description of the Drawings

The invention will be better understood by reference to the following description of one specific embodiment thereof, as shown in the accompanying drawings in which:

Figure 1 is a schematic view of a gaseous fuel direct injection system according to the embodiment; and

Figure 2 is a graphical representation of the emptying scenario of a fuel tank in the fuel system according to the embodiment.

Best Mode(s) for Carrying Out the Invention

The embodiment shown in the drawings is directed to a gaseous fuel direct injection system 10 for an internal combustion engine of a vehicle (not shown). The arrangement is suitable for a range of vehicles from smaller vehicles such as an auto-rickshaw of the type commonly used in India to heavy duty trucks.

The gaseous fuel direct injection system 10 comprises a gas vessel providing a primary fuel tank 13 for receiving a gaseous fuel such as LPG. The fuel system 10 further comprises a secondary fuel tank (not shown) for receiving a reserve fuel supply which may comprise a gaseous fuel or a conventional liquid fuel (such as petrol or diesel, according to the fuel cycle under which the engine operates).

If the gaseous fuel comprises a liquefied gas fuel such as liquefied petroleum gas (LPG) or liquefied natural gas (LNG), it is stored in a liquefied state in the tank 13.

The gaseous fuel is delivered to a fuel rail 15 along a fuel line 17. A pressure regulator 19 is incorporated in the fuel supply line 17 to regulate the supply pressure of gaseous fuel to the fuel rail 15. A heat exchanger 21 is also incorporated in the fuel supply line 17 for vaporising liquefied gas fuel so that the gaseous fuel is delivered to the fuel rail 15 in a gaseous state. In the arrangement illustrated, the regulator 19 and the heat exchanger 21 are configured as an integral unit. The fuel supply line also incorporates a filter 25 and a solenoid lock- off valve 27. In this embodiment the engine is a multi-cylinder engine and the gaseous fuel is injected directly into combustion chambers defined by the various cylinders through fuel injectors 23 connected to the fuel rail 15.

Operation of the fuel injectors 23 is controlled by an electronic control unit (not shown). The electronic control unit (ECU) can control the operating parameters of each fuel injector 23, particularly the duration of the opening of the injector, as well as the points in the engine cycle at which the injector is opened and closed.

The ECU receives input signals from various sensors providing information relating to the operating conditions of the engine and driver demands. The ECU outputs various control signals, including in particular control signals relating to operation of the fuel injectors 23.

As the gaseous fuel available in the primary tank 13 depletes, the vapour pressure in the fuel rail 15 diminishes. The ECU is able to compensate for the reduced vapour pressure in the fuel rail 15 by controlling the quantity of gaseous fuel delivered by the fuel injectors 23 through variation of the operating parameters of the fuel injectors. The ECU varies the operating parameters of each fuel injector 23 by controlling the duration of opening of the fuel injector, the time at which the fuel injector begins to open relative to the engine cylinder cycle, the time at which the fuel injector begins to close relative to the engine cylinder cycle, or any combination thereof. Specifically, the ECU increases the duration of opening of the fuel injectors 23 as necessary in order to maintain delivery of a necessary mass of gaseous fuel into the combustion chambers as required for prevailing engine operating conditions.

At some stage the ECU can no longer compensate for the reduced fuel pressure, at which time it becomes necessary to switch the fuel supply from the primary tank 13 containing the gaseous fuel to the secondary tank (not shown). This is necessary as it is not desirable to continue to operate the engine in the absence of adequate fuel availability, as there will be a reduction in engine power, lean air- to-fuel ratios and poor driveability. However, it is also desirable to optimise use of the gaseous fuel available in the primary tank 13. Accordingly, there is a need to detect when it is imminent that there is no longer adequate gaseous fuel available in the primary tank 13 to continue to operate the engine satisfactorily and only then switch to the reserve fuel supply. To this end, the gaseous fuel vapour pressure in the primary fuel tank 13 and the gaseous fuel vapour pressure in the fuel rail 15 are continually monitored, with any reduction over a relatively short period of time being indicative of imminent insufficiency of available fuel.

For this purpose, the sensors for providing information to the ECU include a first sensor 31 for sensing the vapour pressure of the gaseous fuel contained in the fuel tank 13, and a second sensor 32 for sensing the vapour pressure of the gaseous fuel within the fuel rail 15. The first sensor 31 also senses the temperature of the gaseous fuel contained in the fuel tank 13 and the second sensor 32 also senses the temperature of the gaseous fuel in the fuel rail 15. The temperature sensing capability provides additional advantages for certain gaseous fuels, as will be explained later.

The data collected in relation to the gaseous fuel vapour pressure in the primary fuel tank 13 and the gaseous fuel vapour pressure in the fuel rail 15 is stored temporarily in the ECU memory for a given engine speed and engine load. Typically, this is done each engine cycle, but other timing arrangements are possible. New pressure data is compared, typically on a continuous basis multiple times per second, although other timing arrangements are possible. If the change in the gaseous fuel vapour pressure in the primary fuel tank 13 and/or the gaseous fuel vapour pressure in the fuel rail 15 reduces faster than a calibrated rate then the primary fuel tank 13 is considered to be empty.

This monitoring strategy will be better understood with reference to Figure 2 which is a graphical representation of the fuel tank emptying scenario, showing: (1) the gaseous fuel vapour pressure in the primary fuel tank 13 (identified as TANK); (2) the gaseous fuel vapour pressure in the fuel rail 15 (identified as RAIL); (3) the duration of opening of the respective fuel injector 23 (identified as FPW, being fuel pulse width); and (4) the air-to-fuel ratio (identified as AFR). Referring to Figure 2, the stage identified as A represents the point at which the gaseous fuel vapour pressure in the primary fuel tank 13 commences to reduce, and the gaseous fuel vapour pressure in the fuel rail 15 also commences to reduce because of the characteristics of the pressure regulator 19. At this stage the duration of opening of the fuel injectors 23 commences to increase in order to maintain delivery of a necessary mass of gaseous fuel into the combustion chambers, thereby compensating the fuelling for the reducing gaseous fuel vapour pressure in the fuel rail 15. The stage identified as B represents the point at which the maximum limit of compensation of the duration of opening of the fuel injectors 23 is reached. After this point, further compensation of the fuel injector opening duration to account for reducing fuel rail pressure is not effective and the required mass of gaseous fuel for an engine operating cycle cannot be delivered into the combustion chambers, with the result that the AFR increases to unacceptable levels and becomes lean. The stage identified as C represents the limits of combustion stability, at which engine driveability is unsatisfactory. The ^' stage identified as D represents the point at which the engine will stall through lack of fuel.

In terms of the monitoring performed by the ECU, the ECU recognises the slope of the TANK and RAIL plot lines prior to reaching stage B and initiates a switch to the reserve fuel supply.

In other words, the ECU recognises a change in the operating characteristics while the engine is operating and initiates action in response thereto, which in this embodiment involve switching the fuel supply from the primary fuel tank 13 to the secondary fuel tank.

The ECU may also initiate a signal of any appropriate form for the operator of the engine (such as a visual signal and/or an audible signal) indicating the switch of the fuel supply from the primary fuel tank 13 to the secondary fuel tank.

As alluded to above, the temperature sensing performed by the first sensor 31 and the second sensor 32 provides additional advantages for certain gaseous fuels, as in conjunction with the pressure sensing it allows the composition of such fuels to be evaluated and fuelling compensated for significant variations that might occur. This is advantageous as the composition of some gaseous fuel mixtures can vary according to the source and also the season of the year. The variation in composition of gaseous fuels can affect the mass flow rate, calorific value and stoichiometric ratio of the fuel. This in turn can impact upon the performance of the engine, particularly in relation to the emission levels, torque, combustion stability and driveabliity in the case of engines for vehicles. By way of example, varieties of LPG available include mixtures that are primarily propane, mixtures that are primarily butane, and more commonly mixtures including both propane and butane. Similarly, the composition of natural gas (which is primarily methane) can vary, as can the compositions of blended gaseous fuels (typically hydrogen and natural gas). The ECU refers to a "look-up" map or table to determine the composition of the gaseous fuel according to the temperature and vapour pressure of the gaseous fuel stored in the fuel tank 13. From the foregoing, it is evident that the invention provides a simple yet highly effective way of determining the stage at which it becomes necessary to switch the fuel supply from the primary tank containing the gaseous fuel to the secondary tank. The ECU recognises a change in the operating characteristics while the engine is operating and initiates action in response thereto, switching the fuel supply from the primary tank containing the gaseous fuel to the secondary tank. In particular, the decaying pressure characteristic of the depleting gaseous fuel in the primary fuel tank 13 is utilised to recognise the stage at which the ECU can no longer compensate for the reduced gaseous fuel pressure and at which it is necessary to switch the fuel supply to the secondary tank.

It should be appreciated that the scope of the invention is not limited to the scope of the embodiment described.

By way of example, the invention is not limited to direct injection systems. The invention may be applied in systems that rely on port injection or fumigation (whether the fuel is metered by injectors or other metering devices such as, for example, servoids).

The invention may be applied to gaseous fuel delivery systems likely to be used on heavy duty on-highway diesel engines and associated vehicles. Further, while the embodiment has been described in relation to an arrangement where there is one fuel injector for each engine cylinder, the invention need not be limited thereto. For example, the invention may have application to arrangements where the number of injectors does not equal the number of cylinders.

Further, the invention may not be limited to an arrangement where injection operation is synchronous with engine timing.

The invention may have application to engines operating under two-stroke or four- stroke cycles.

Further, the invention may have application to both compression ignition and spark ignition engines. Still further, the invention may be used in relation to a two-fluid fuel injection system in which fuel is delivered to a combustion chamber by way of a compressed gas such as air.

Throughout the specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.