Dual fuel conversion

Dual Fuel Conversion

Field of the Invention

This invention relates to internal combustion engines configured for dual fuel operation. The invention has particular applicability where engines configured to run on a primary or standard fuel can be adapted to also run on a secondary or alternative fuel.

More particularly, the invention relates to injection of fuels in internal combustion engines for dual fuel operation, wherein one of the fuels comprises a gaseous fuel which is delivered to the engine in a liquid phase. Liquefied gaseous fuels suitable for liquid phase injection include liquefied petroleum gas (LPG) and liquefied natural gas (LNG).

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.

The invention is particularly applicable to liquid phase injection (LPI) of gaseous fuels such as LPG. Accordingly, the invention will be discussed in relation to operation of an engine involving liquid phase injection (LPI) of gaseous fuels such as LPG, although the invention need not be restricted to such fuels.

For the LPI process, it is necessary to deliver liquefied gaseous fuel to a fuel injector in the liquid phase.

The liquefied gaseous fuel is delivered through fuel injectors configured for either direct injection of fuel or indirect injection of fuel. For direct injection, the fuel injectors deliver fuel directly into combustion chambers of an engine. With this delivery arrangement, the fuel injectors typically communicate with ports in the respective engine cylinders. For indirect injection, the fuel injectors deliver fuel at some point before the engine intake valves, typically into an air inlet manifold. With this delivery arrangement, the fuel injectors typically communicate with ports in the inlet manifold.

Many engines are configured for direct injection of a dedicated fuel, such as gasoline, with fuel injectors for delivering the fuel arranged within ports in the respective engine cylinders, with the fuel injectors operating under the control of a control system which typically comprises an electronic control unit (ECU). The ECU determines the parameters by which the fuel injectors operate. In particular, the ECU can control the duration of the opening of each fuel injector, the time at which the fuel injector begins to open relative to the engine operating cycle, and the time at which the fuel injector begins to close relative to the engine operating cycle. The ECU obtains input signals from various sensors providing information on the operating conditions of the engine as well as the driver demands, and outputs control signals to certain engine components. The fuel injection system typically includes means for monitoring the pressure of fuel supplied to the fuel injectors. The engine ECU is able to modify the injector control parameters to control delivery through the fuel injectors with differing fuel pressures and to hence vary the flow of fuel through the fuel injectors. The injector control parameters include start of injection angle and injection duration. Typically, the fuel pressure is determined by a pressure sensor installed in the fuel rail of the fuel injection system, with the sensor providing an input signal to the ECU.

For engines configured for dual fuel operation, fuel injectors for a first fuel are typically arranged with respect to the engine cylinders to provide direct injection into the corresponding engine combustion chambers and so typically a further set of fuel injectors for a second fuel cannot also be incorporated for direct injection in to the engine cylinders. Consequently, the delivery system for the second fuel is typically configured for indirect injection, with the fuel injectors for the second fuel delivering the second fuel at some point before the intake valve, typically into an air inlet manifold. It certain applications, it would however be advantageous to use a common set of fuel injectors for selective delivery of the two fuels, with the fuel injectors being switched between the two fuels as necessary.

However, owing to different characteristics of the two fuels (particularly differences in energy content), it is invariably necessary for the fuel injectors to be controlled differently in terms of timing of their operation for the accurate metering and delivery of the fuels. Accordingly, the ECU typically cannot be used to control the fuel injectors for common operation with both fuels.

Accordingly, this presents difficulties in relation to the use of a common set of fuel injectors for the selective delivery of the two fuels, whether the fuel injectors are arranged for direct injection or indirect injection of the fuel the engine cylinders.

Consequently, conversion of a direct injection internal combustion engine to dual fuel operation would normally require that a fuel delivery system configured as an indirect injection system be retrofitted for delivery of the second fuel in addition to the existing direct injection fuel system.

There have been several proposals involving use of common set of fuel injectors for the selective delivery of the two fuels.

One such proposal is disclosed in US2002/0195088 (Oprea) which is directed to a dual fuel system for feeding a main fuel and a secondary fuel to an internal combustion engine. The dual fuel system utilises a common fuel injector connected to two separate fuel circuits, one for the main fuel and the other for the secondary fuel. Each fuel circuit has a separate fuel rail to which the common fuel injector is connected. The fuel injector has two separate fuel paths isolated from each other and each communicating with a respective fuel rail. Such an arrangement is disadvantageous as it requires two separate fuel rails and a dedicated fuel injector configured to provide two separate fuel paths.

Another proposal involving use of a common set of fuel injectors for the selective delivery of the two fuels is disclosed in US 6,035,837 (Cohen et al) and is directed at a bi-fuel injection system for selectively suppling two different fuels to an internal combustion engine by way of an indirect injection process using a single fuel rail and common injectors. The bi-fuel injection system disclosed is directed to an arrangement in which the fuel rail and fuel injectors are capable of receiving either fuel such that one of the fuels is continuously flowing through the injectors during operation of the engine and which purges residual fuel when switched from one fuel to the other. The bi-fuel injection system incorporates an electronic control unit (ECU) for controlling its operation, including switching between the two fuels, and determining the fuelling requirements for the engine on an ongoing basis and operating the fuel injectors accordingly. Such an arrangement requires an ECU dedicated to controlling the fuel injectors according to the selected fuelling regime, and also a fuel rail and fuel injectors configured to receive either fuel such that one of the fuels can flow continuously through the fuel injectors during operation of the engine and residual fuel can be purged upon switching from one fuel to the other.

Yet another proposal involving use of a common set of fuel injectors for the selective delivery of the two fuels is disclosed in US 5,379,740 (Moore et al) and is directed at a dual fuel injection arrangement for selectively suppling two different fuels to an internal combustion engine by way of an indirect injection process. The dual fuel injection arrangement uses a single fuel rail and common injectors which are connected to the fuel rail to receive fuel from a fuel supply and also connected to a return line for returning excess fuel to the supply. An electronic control arrangement is provided for controlling the injection of fuel into the engine. The electronic control arrangement comprises two separate electronic control units which determine injection timing for the selected fuel dependent upon engine parameters for the first fuel and upon an adjusted timing for the second fuel, with the adjustment taking account of the different characteristics of the second fuel with respect to the first fuel. In particular, the injection timing characteristics for the first fuel are determined and converted to the correct timing characteristics for the second fuel dependent upon the energy characteristics of the second fuel and the pressure of the second fuel. The first electronic control unit is configured to control injection of the first fuel and the second electronic control unit is configured to convert the injection timing for the first fuel into the injection timing for the second fuel upon a switch to the second fuel. When the dual fuel injection arrangement is being operated to supply the first fuel, injection signals generated by the first electronic control unit are routed through the second electronic control unit without being changed. When the dual fuel injection arrangement is being operated to supply the second fuel, injection timing signals for the first fuel are transmitted from the first electronic control unit to the second electronic control unit at which they are converted to injection timing signals for the second fuel. The conversion is calculated or determined from lookup tables having regard to the pressure of the second fuel and possibly other characteristics of the second fuel such as temperature. With this arrangement, the relationship between the first and second electronic control units is such that the second electronic control unit merely receives input data from the first control unit and controls operation of the fuel injectors according to the fuel type and desired fuelling requirements. There is no further interaction between the two control units. Accordingly, the dual fuel injection arrangement is an integrated system which is not conducive to being retrofitted to an engine originally configured for operation using a single fuel for conversion of that engine into one capable of dual fuel operation.

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

According to a first aspect of the invention there is provided a method for delivering a secondary fuel for use by an internal combustion engine, the method comprising providing a supply of the secondary fuel, delivering a metered quantity of the secondary fuel to the engine through a fuel injector operating under the control of a control means adapted to receive a fuel pressure input indicative of the fuel pressure, and substituting the indication of the fuel pressure when the secondary fuel is being delivered through the fuel injector with a substitute input causing the control means to operate the fuel injector in a timing regime appropriate for the secondary fuel. Preferably, the fuel injector is arranged to facilitate the direct injection of the primary fuel and the secondary fuel into a combustion chamber of the engine. Preferably, the primary fuel is a liquid fuel and the secondary fuel is a gaseous fuel which is delivered in a liquid phase to the combustion chamber.

According to a second aspect of the invention there is provided a method for the liquid phase injection of a gaseous fuel directly into a combustion chamber of an internal combustion engine, the method comprising providing a supply of gaseous fuel, delivering a metered quantity of gaseous fuel in a liquid phase into the combustion chamber through a fuel injector operating under the control of a control means adapted to receive a fuel pressure input indicative of fuel pressure, and substituting the indication of fuel pressure when gaseous fuel is being delivered in liquid phase through the fuel injector with a substitute input causing the control means to operate the fuel injector in a timing regime appropriate for the liquid phase injection of the gaseous fuel.

With this arrangement, the control means expects to receive a fuel pressure input indicative of the primary liquid fuel pressure. However, the control means actually receives the substitute input and perceives it as the expected fuel pressure input for the primary fuel and responds accordingly. In other words, the substitute input mimics the fuel pressure input but in a form commensurate with operation of the fuel injector in a manner appropriate for liquid phase injection of the gaseous fuel, and the control means is essentially "tricked" into operating the fuel injector in a manner dictated by the substitute input. In effect, the substitute input "tricks" the control means into operating the fuel injector in a manner appropriate for liquid phase injection of the gaseous fuel.

Preferably, the control means comprises as a primary electronic control unit (ECU). The control means may comprise an OEM ECU for the engine. Preferably, there is provided a supplementary control means adapted to intercept and interfere with certain signals associated with the primary electronic control unit. The supplementary control means may comprise a supplementary ECU.

Preferably, the method further comprises selective operation of the engine in a liquid fuel mode, whereby the primary liquid fuel is delivered directly into the combustion chamber of the engine. Preferably, the supplementary control means is operable to control the fuel setting according to whether the fuelling requirement is the primary liquid fuel or liquid phase injection of the gaseous fuel.

Preferably, the supplementary control means is configured to intercept the fuel pressure input and to deliver a corresponding interception signal to the primary ECU. The interception signal is perceived by the primary ECU to be an expected fuel pressure input for the primary liquid fuel but it is in fact a signal generated by the supplementary ECU to cause the primary ECU to operate the fuel injector in a manner designated by the supplementary ECU and suitable for the liquid phase injection of the gaseous fuel. In other words, the supplementary ECU "tricks" the primary ECU to operate the fuel injector in a manner designated by the supplementary ECU.

Further, the supplementary ECU is configured to intercept the control signals from the primary ECU and relay them to the fuel injector. With this arrangement, the fuel injector can be used as a common fuel injector for the selective delivery of either the primary liquid fuel or the gaseous fuel in a liquid phase.

When the fuelling requirement for the engine is gaseous fuel, the supplementary control means sets a fuel selection valve for delivery of the gaseous fuel in a liquid phase to a fuel rail to which the fuel injector is connected. The supplementary control means samples pressure signals from a pressure sensor associated with the fuel rail and also samples injector control signals from the primary control means. The supplementary control means then calculates engine speed from the injector control signals and the notional primary liquid fuel demand corresponding thereto. From the notional primary liquid fuel demand, the supplementary control means calculates the required gaseous fuel demand corresponding to the notional primary liquid fuel demand. The supplementary control means then determines the change in the operating parameters of the fuel injector in order to deliver the required amount of gaseous fuel in a liquid phase. The change in the operating parameters typically involves earlier start of the injection angle in order to complete injection at about the same end of injection angle. The supplementary control means then references a suitable function, look-up table, or map to identify the interception signal to be sent to the primary control means. The interception signal is perceived by the primary control means to be the expected signal from the pressure sensor but it is in fact a signal generated by the supplementary control means to cause the primary control means to operate the fuel injector in a manner reflecting the required change in operating parameters to deliver the required amount of gaseous fuel in its liquid phase. The interception signal is such that it reflects the corresponding pressure signal required to be fed to the primary control means to cause the latter to operate the fuel injector in the manner required to deliver the required amount of gaseous fuel in its liquid phase. Accordingly, the primary control means generates injector control parameters consistent with the manner in which the fuel injector is required to operate in order to deliver the required amount of gaseous fuel in liquid phase. The supplementary control means receives the modified injector control parameters and relays them to the fuel injector, thereby causing the fuel injector to operate in the modified manner.

According to a third aspect of the invention there is provided a method of selectively supplying a first fuel and a second fuel from respective fuel sources to a combustion chamber of an internal combustion engine, the method comprising providing a common fuel rail to selectively supply one of the first and second fuels to a fuel delivery injector operating under the control of a control means; providing a valve operable for selectively communicating each of the fuel sources with the fuel rail; providing the control means with a fuel pressure input indicative of the pressure of the selected fuel; and causing the control means to operate the fuel injector in a regime appropriate for the selected fuel; wherein when the selected fuel comprises the second fuel the method further comprises substituting the indication of the fuel pressure when the second fuel is being delivered through the fuel injector with a substitute input causing the control means to operate the fuel injector in a regime appropriate for the second fuel. According to a fourth aspect of the invention there is provided an internal combustion engine configured for operation in accordance with the method according to the first, second or third aspect of the invention.

According to a fifth aspect of the invention there is provided a dual fuel system for fuelling an internal combustion engine, the dual fuel system comprising a primary fuel system for injection of a metered quantify of a primary fuel to the engine and a secondary fuel system for injection of a metered quantify of second fuel to the engine, the two fuel systems being configured for selective direct injection of the respective fuel through a common fuel injector. Preferably, the primary fuel is a liquid fuel and the secondary fuel is a gaseous fuel which is delivered in a liquid phase to the combustion chamber.

Preferably, the primary fuel system has a primary control means, and the dual fuel system further comprises a supplementary control means adapted to intercept and interfere with certain signals associated with the primary control means. Typically, the primary control means comprises the OEM ECU for the engine.

According to a sixth aspect of the invention there is provided a dual fuel system for fuelling an internal combustion engine, the dual fuel system comprising a liquid fuel system for injecting a metered quantify of a primary liquid fuel into a combustion chamber of the engine and a gaseous fuel system for liquid phase injection of a metered quantify of gaseous fuel into a combustion chamber of the engine, the two fuel systems being configured for direct injection of the respective fuel into the combustion chamber through a common fuel injector.

According to a seventh aspect of the invention there is provided a dual fuel system for fuelling an internal combustion engine, the dual fuel system comprising a fuel injector for delivering fuel into a combustion chamber of the engine, a fuel rail for selectively delivering a first fuel and a second fuel to the fuel injector, control means for operating the fuel injector in a timing regime appropriate for the selected fuel, the control means comprising a first control unit and a second control unit, wherein the first control unit is operable to determine the timing regime for operation of the injector for delivery of the first fuel in response to an indication of the fuel pressure and wherein the second control unit is operable to deliver a substituted indication of fuel pressure to the first control means when the second fuel is being delivered through the fuel injector, the substituted indication causing the control means to operate the fuel injector in a timing regime appropriate for the second fuel.

Preferably, the fuel injector is configured for delivering fuel directly into a combustion chamber of the engine; that is, the dual fuel system is configured for direct injection.

The internal combustion engine may comprise a multi-cylinder engine having a corresponding number of combustion chambers and fuel injectors, the fuel injectors each being connected to the fuel rail to receive fuel therefrom. With this arrangement, the fuel rail is common to all of the fuel injectors.

Preferably, the dual fuel system further comprises a fuel selection valve operable for selectively communicating the fuel rail with respective sources of the first and second fuels.

According to an eighth aspect of the invention there is provided a conversion system for modifying an internal combustion engine fitted with a direct injection liquid fuel delivery system to a dual fuel system so that the engine can selectively operate on a primary liquid fuel or a secondary gaseous fuel, the dual fuel system comprising a liquid fuel system for directly injecting a metered quantify of the primary liquid fuel into a combustion chamber of the engine and a gaseous fuel system for the direct liquid phase injection of a metered quantify of gaseous fuel into a combustion chamber of the engine, the two fuel systems being configured for injection of the respective fuel into the combustion chamber through a common fuel injector.

Typically, the common fuel injector comprises the fuel injector used in the liquid fuel delivery system prior to modification thereof.

According to a ninth aspect of the invention, there is provided an internal combustion engine fitted with a dual fuel system according to the fifth, sixth or seventh aspect of the invention. According to a tenth aspect of the invention, there is provided an internal combustion engine fitted with a conversion system according to the eighth 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 in which:

Figure 1 is a schematic view of a direct injection liquid fuel delivery system for an internal combustion engine prior to modification thereof to a dual fuel system according to the embodiment; Figure 2 is a schematic view of a dual fuel direct injection system according to the embodiment involving modification of the direct injection liquid fuel delivery system shown in Figurel ; and

Figure 3 is a flowchart depicting the process implemented by an engine control module for operation of the dual fuel direct injection system according to the embodiment.

Best Mode(s) for Carrying Out the Invention

The embodiment is directed to an aftermarket conversion of an internal combustion engine fitted with a direct injection liquid fuel delivery system to a dual fuel system so that the engine can selectively operate on a primary liquid fuel or a secondary fuel. In this embodiment, the primary liquid fuel comprises gasoline and the secondary fuel comprises a liquefied gaseous fuel which is delivered to the engine in a liquid phase. The liquefied gaseous fuel comprises LPG.

In Figure 1 there is shown the direct injection liquid fuel delivery system 11 in the OEM condition. The direct injection liquid fuel delivery system 11 is configured for a multi-cylinder engine and comprises a liquid fuel supply line 13 adapted to receive liquid fuel from a fuel tank (not shown). The liquid fuel delivery system 11 further comprises a plurality of liquid fuel direct injectors 15 operable to deliver metered quantities of the primary liquid fuel to the combustion chambers within the engine cylinders (not shown) in timed sequence. The fuel injectors 15 are incorporated in a fuel rail assembly 17.

The fuel injectors 15 are operable in response to control signals received from an engine control unit (ECU) 21. The operation of the fuel injectors 15 is controlled in terms of the timing of opening, and the duration of opening, of the injectors.

The ECU 21 obtains input signals from various sensors providing information on the operating conditions of the engine as well as the driver demands, and outputs control signals to certain engine components.

The direct injection liquid fuel delivery system 11 includes means for monitoring the pressure of fuel supplied to the fuel injectors 15 and modifying the flow through the injectors 15 to accommodate pressure fluctuations. The ECU 21 is able to modify the injector control parameters to control delivery through the fuel injectors 5 with differing fuel pressures and to hence vary the flow of fuel through the fuel injectors 15. The injector control parameters include start of injection angle and injection duration. For example, in certain circumstances, the modification to flow may involve advancing the timing of the injection in circumstances where there is an increase in the fuel pressure, and retarding the timing of the injection in circumstances where there is a decrease in the fuel pressure. The fuel pressure is determined by a pressure sensor 23 installed in the fuel rail assembly 17, with the sensor 23 providing an input signal to the ECU 21.

By way of an aftermarket conversion, the arrangement shown in Figure 1 is modified to provide the arrangement shown in Figure 2, being a dual fuel direct injection system 30 according to the embodiment. The modification to provide the dual fuel direct injection system 30 in this embodiment involves installation of a gaseous fuel supply 33 comprising a source (not shown) such as a pressurized tank or other reservoir and a delivery line 35.

The delivery line 35 communicates with a fuel selection valve 37 installed in the liquid fuel supply line 13. With this arrangement, either liquid fuel or a liquid phase of the gaseous fuel (which is under pressure to maintain the liquid phase in the delivery line 35) can be selectively delivered to the fuel rail assembly 17 and the fuel injectors 15, according to the setting of the fuel selection valve 37.

The modification further involves installation of a supplementary control means 41 in the form of a the supplementary ECU, which will hereinafter be referred to a "piggy back" ECU for the reason that it operates in conjunction with the OEM ECU 21 and intercepts and interferes with certain signals associated therewith, as will be explained later.

The "piggy back" ECU 41 controls the setting of the fuel selection valve 37 according to whether liquid fuel or gaseous fuel operation is required. Further, the "piggy back" ECU 41 is configured to intercept signals from the pressure sensor 23 installed in the fuel rail assembly 17 and to deliver a corresponding interception signal to the OEM ECU 21. The interception signal is perceived by the OEM ECU 21 to be an expected signal from the pressure sensor 23 but it is in fact a signal generated by the "piggy back" ECU 41 to cause the OEM ECU 21 to operate the fuel injectors 15 in a manner designated by the "piggy back" ECU 41. In other words, the "piggy back" ECU 41 "tricks" the OEM ECU 21 into operating the fuel injectors 15 in a manner designated by the "piggy back" ECU 41.

Further, the "piggy back" ECU 41 intercepts the control signals from the OEM ECU 21 and relays them to the fuel injectors 15.

With this arrangement, the fuel injectors 15 can be used as common fuel injectors for selective delivery of either the liquid fuel or a liquid phase of the gaseous fuel.

In delivering a liquid phase of the gaseous fuel, the operating parameters of the fuel injectors 15 are modified to deliver the gaseous fuel in the required amount and at the required rate.

When the primary liquid fuel is required, the "piggy back" ECU 41 sets the fuel selection valve 37 accordingly. The "piggy back" ECU 41 samples pressure signals from the pressure sensor 23 and also samples injector control signals from the OEM ECU 21. The "piggy back" ECU 41 then outputs a signal to the OEM ECU 21 indicative of the actual fuel rail pressure. The OEM ECU 21 generates the corresponding fuel injector control parameters which are intercepted by the "piggy back" ECU 41 and relayed to the fuel injectors 15 without modification. The fuel injectors 15 operate under the control of the un- modified control parameters and thus deliver metered quantities of the primary liquid fuel in the usual way.

When gaseous fuel is required, the "piggy back" ECU 41 sets the fuel selection valve 37 accordingly. The "piggy back" ECU 41 samples pressure signals from the pressure sensor 23 and also samples injector control signals from the OEM ECU 21. The "piggy back" ECU 41 then calculates engine speed from the injector control signals and the notional primary liquid fuel demand corresponding thereto. From the notional primary liquid fuel demand, the "piggy back" ECU 41 calculates the required gaseous fuel demand corresponding to the notional primary liquid fuel demand. The "piggy back" ECU 41 then determines the change in the operating parameters of the injectors 15 in order to deliver the required amount of gaseous fuel in a liquid phase. The change in the operating parameters typically involves earlier start of the injection angle in order to complete injection at about the same end of injection angle. The "piggy back" ECU 41 then references a suitable function, look-up table, or map to identify the interception signal to be sent to the OEM ECU 21. The interception signal is perceived by the OEM ECU 21 to be the expected signal from the pressure sensor 23 but it is in fact a signal generated by the "piggy back" ECU 41 to cause the OEM ECU 21 to operate the fuel injectors 15 in a manner reflecting the required change in operating parameters to deliver the required amount of gaseous fuel in its liquid phase. The interception signal is such that it reflects the corresponding pressure signal required to be fed to the OEM ECU 21 to cause the latter to operate the fuel injectors 15 in the manner required to deliver the required amount of gaseous fuel in its liquid phase. Accordingly, the OEM ECU 21 generates injector control parameters consistent with the manner in which the fuel injectors 15 are required to operate in order to deliver the required amount of gaseous fuel in liquid phase. The "piggy back" ECU 41 receives the modified injector control parameters and relays them to the fuel injectors 15, thereby causing the fuel injectors 15 to operate in the modified manner.

The control strategy as described above is outlined in the flowchart in Figure 3 depicting the process implemented by the "piggy back" ECU 41 operating in conjunction with the OEM ECU 21.

From the foregoing, it is evident that the present embodiment allows for aftermarket conversion of an internal combustion engine fitted such that it can operate with a single set of injectors to deliver two different fuels to an engine. More specifically, the present embodiment allows for aftermarket conversion of an internal combustion engine fitted with a direct injection liquid fuel delivery system to a dual fuel system so that the engine can selectively operate on the primary liquid fuel or a secondary fuel and use common fuel injectors, particularly where the secondary fuel is a gaseous fuel delivered to the engine in a liquid phase.

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 an aftermarket conversion application. The invention could be applied to an OEM application, providing an effective way for an OEM engine to be supplied in a dual fuel configuration, requiring little infrastructure change and in particular not requiring replacement of the OEM ECU. Furthermore, the invention could be applied such that once a conversion has been effected, an engine originally configured to run solely on a primary liquid fuel could be capable of running exclusively on a secondary fuel, such as gaseous fuel delivered to the engine in a liquid phase.

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.