WO1989000640A1

WO1989000640A1 - Improvements in or relating to fuel injection

Info

Publication number: WO1989000640A1
Application number: PCT/GB1988/000558
Authority: WO
Inventors: Timothy James Bedford
Original assignee: Gaspower Limited
Priority date: 1987-07-10
Filing date: 1988-07-11
Publication date: 1989-01-26
Also published as: AU2087888A

Abstract

An L.P.G. flow control injector housing assembly (1) has a central valve part (12) leading to injector nozzle (13) and L.P.G. at the bottom of chamber (18) (introduced via bores 14, 15, 16, 17 from chamber 11) is fed back on itself through bore (19). Vapourising of L.P.G. on exit from nozzle (13) provides a cooling effect in and around manifold (4), which induces a pre-cooling effect on the L.P.G. still in a liquid state in chamber (18). A temperature probe (t.p.) is placed in the chamber (20) and conveys temperature information to an electronics control device (E.C.D.1) which determines the constituent mix of the L.P.G. and pulses the injector solenoid via line (p.s.) accordingly for efficient running of a dual fuel engine which the L.P.G. injector serves. The control device (E.C.D.1.) is utilised in conjunction with a control device (A.E.C.D.) which is already used in running of the engine on petrol. The addition of the device (E.C.D.1) and L.P.G. injector(s) thus allows the petrol engine to run on L.P.G. and utilises signal information from engine condition sensors S1' to S5', already provided for running on petrol, also to control running of the engine on L.P.G. by way of the device (E.C.D.1).

Description

IMPROVEMENTS IN OR RELATING TO FUEL INJECTION

This invention relates to improvements in or relating to fuel injection of L.P.G. (Liquid petroleum gas) into engines originally designed or adapted to run on L.P.G.

Problems exist in achieving the adequate delivery of L.P.G. fuel to engines (usually motor vehicle engines), more particularly under varying operating conditions and also when the nature of the constituent parts of the L.P.G. fuel are inconsistent. In some countries such as Holland and Japan vehicles which run on L.P.G. are now well established but constituents of the L.P.G. obtainable from fuel stations can vary considerably in the proportions of butane to propane and this factor needs to be catered for in injecting the L.P.G in an efficient manner. Popularity of motor vehicle engines running on L.P.G. is on the increase but there are still other problems in providing efficient, cost effective L.P.G. injection to suit the needs of the modern driver. Additional problems exist in providing a quick enough response time more particularly on throttle opening from low speed. There are also further problems in converting, in a satisfactory and economical manner, engines designed for petrol injection so as to run on L.P.G.

It is an object of the present invention to provide apparatus and methods for injecting L.P.G. fuel into an engine in which one or more of the aforementioned problems is/are at least alleviated.

According to one aspect of the present invention there is provided apparatus comprising at least one

L.P.G. fuel injector having a temperature measuring device or probe located, in use, preferably adjacent an exit aperture of a nozzle of said fuel injector device, said measuring device or probe being arranged to sense the vapourizing temperature of L.P.G. liquid exiting said aperture and to relay temperature information to a control device issuing control signals to regulate the supply of L.P.G. via said injector device.

Further according to this aspect of the present invention there is provided a method of controlling or modifying the regulation of L.P.G. supply to an internal combustion engine from an L.P.G. flow control injector device or devices depending upon the proportion of at least some of the constituent parts (normally, the proportion of propane to butane) of the L.P.G. mix, said method comprising:- sensing the temperature of vapourisation of the L.P.G. and relaying temperature information to a control device for issuing control signals to regulate the supply of L.P.G. from the injector device or devices.

Usually the temperature information will be evaluated in an electronics control device already used to regulate the supply of L.P.G. via the or each injector device, and the latter will usually comprise solenoid actuated valve means arranged for pulsing operation so as to act as an L.P.G flow controller. The pulsing signals already sent to the injector device or devices may be modified by way of said temperature information and by said electronics control device in order to vary the opening time of the solenoid valve means thereby to provide a more efficient running of an internal combustion engine fitted with such injector or injectors.

Other advantageous features of this aspect of the present invention will be apparent from the following description and drawings. In particular, the flow control injector itself may be of the general form later described and (also as later described) the L.P.G. fuel is, most preferably, pre-cooled before exiting the nozzle aperture. It is believed that a tubular injector device configuration generally as shown in the accompanying drawings and provision for the liquid L.P.G. to surround cooling, vapourizing L.P.G. is a particularly effective and convenient way of achieving this pre-cooling.

According to a second aspect of the present invention there is provided apparatus comprising an L.P.G. fuel flow control injector device or devices and a first electronics control device utilisable: in conjunction with an existing electronics control device, said latter device being for controlling the running of an internal combustion engine designed to run on a fuel other than L.P.G., for example petrol or diesel, and/or utilisable in conjunction with a sensor array used to supply information to said existing electronics control device, said apparatus being able by way of said utilisation to control the injection of L.P.G. into an internal combustion engine in accordance with engine requirements.

Further according to said second aspect of the present invention there is provided a method of injecting L.P.G. into an internal combustion engine comprising utilising: control signals from an existing electronics control device and/or from an existing sensor array in or for an internal combustion engine designed to run on a fuel other than L.P.G. (usually petrol), in order to regulate the supply of L.P.G. through an L.P.G. flow control injector device or devices into said engine. Preferably, by way of this second aspect of the present invention the original fuel supply system

(usually fuel injection) will be undisturbed so that if desired the engine could still be run on its original fuel by way of the original electronics control.

Further advantageous features of this second aspect of the present invention will be evident from the following description and drawings. Of course, in such a system, use may be made of additional sensors feeding signal information, into said first electronics control device and one such sensor may comprise temperature sensor means measuring the temperature of vapourisation of the L.P.G. or temperature difference in vapourisation occurring under a particular pressure drop across the L.P.G. flow control device or devices.

In either of the two aspects of the present invention already discussed provision may be made for improving efficiency at low engine speed. This may be done by programming the electronics control device or devices to momentarily increase the output of the solenoid valve.

According to yet a further aspect of the present invention there is provided apparatus comprising an L.P.G. flow control injector device or devices and an electronics control device for controlling the supply of L.P.G. via said injector device or devices to an internal combustion engine during normal running conditions:- characterised by a second L«P.G. supply to a further solenoid valve actuated at low engine speed, the second supply of L.P.G being fed into an inlet manifold through said injector device or devices and/or further upstream of said injector device or devices.

Further according to this further third aspect of the^" present invention there is provided a method of controlling the injection of L.P.G. into an internal combustion engine at low engine speed by supplying L.P.G. from a second L.P.G. supply line, for example to said L.P.G. injector device or devices or further upstream in the air inlet manifold.

Further advantageous features of this third aspect of the present invention will be evident from the following description and drawings.

Still further according to the present invention there is provided a dual fuel internal combustion engine adapted to operate in a first mode as a petrol injection engine utilising petrol as a fuel injected in metered quantities by petrol injection devices controlled (usually in accordance with established technology) by first electronic control means responsive to signals supplied from a plurality of sensors arranged to monitor various engine conditions during operation, wherein the engine is also adapted to operate in an alternative mode utilising L.P.G. as a fuel injected into the air intake by an L.P.G. flow control injector device or devices controlled by second electronic control means arranged to respond to the signals from at least some of the same said plurality of sensors that, in said first mode, supply the first electronic control means (and wherein preferably the second electronic control means is arranged to respond to signals from the first electronic control means).

Embodiments of apparatus and method in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

FIGURE 1 shows an L.P.G. flow control injector housing assembly;

FIGURE 2 shows further detail views A and B of a component of the assembly;

FIGURE 3 shows detail views C and D of a further component of the assembly;

FIGURE 4 shows a much simplfied schematic view of an arrangement for controlling the injector, and

FIGURE 5 shows a modified schematic arrangement.

Additional FIGURES will be explained and referred to later.

FIGURE 1 shows a flow control injector housing assembly 1 more particularly for injecting L.P.G. via the air intake into cylinders of an internal combustion engine (not shown). The assembly 1 is generally tubular and includes an outer tubular housing 2 having an end cap 3 (see FIGURE 3) at the right-hand end thereof as shown in FIGURE 1 and an outlet manifold 4 (see FIGURE 2) at the opposing end.

The general form of the assembly 1 should be evident from the drawings. Circular grooves 5, 6 at opposed ends of the housing 2 are for receiving circlips to retain the end cap 3 and manifold 4 in place in the housing 2. 0- rings are located in circular grooves 7 to 10 as will be obvious for sealing purposes.

In use, L.P.G. under pressure is fed via tubing through a hole 3a in end cap 3 into the internally stepped generally annular chamber 11 surrounding the central valve part 12 of the injector device leading to an injector nozzle 13. The L.P.G. in chamber 11 is held at a pressure of 100 p.s.i. The L.P.G. passes from chamber 11 through four bores 14,15,16,17 into chamber 18 surrounding the manifold 4. At the bottom of the chamber 18 the L.P.G. is fed back on itself through a relatively small bore 19 in the housing 2., which bore is arranged parallel to the axis of the housing and which continues for most of the length of the housing. The L.P.G. (which is still in a liquid state under pressure) is fed through the passageway 3b in the end cap 3 into the central part 12 of the injector and thus to nozzle 13.

The valve means of the injector device is operated by a solenoid to regulate flow of the liquid L.P.G._. fuel through the nozzle aperture 13a, to an elongate chamber 20 and hence to outlet pipes p (by way of narrow radial bores b) which lead via tubing (not shown) to an inlet manifold (not shown) where the gas is mixed with air before entering an engine cylinder. In this embodiment, rapid vapourisation of the L.P.G. takes place as soon as the fuel passes through the nozzle 13 by reason of the lower pressure in the manifold 4. The vapourising of the L.P.G. on exit from the nozzle 13 provides a cooling effect in and around the manifold 4, which in turn induces a pre-cooling effect on L.P.G. still in a liquid state in the chamber 18 surrounding the manifold. Thus, advantageously, it is ensured that the L.P.G. reaches the nozzle aperture 13a in a liquid state even if it should become overheated and partially vapourised at some earlier point in the supply line. It is important to ensure that the L.P.G. is still in a liquid state when it reaches the nozzle aperture 13a in order to maintain accurate metering and because other problems can occur, for example production of a hydraulic lock in the fuel supply and ice formation at the air intake.

Metered amounts of L.P.G. pass to the pipes p via radial bores b and one bore b is provided for each pipe. The number of pipes p will vary according to the number of engine cylinders (usually four or six) and in the instance shown four bores b are provided leading to four pipes p. In this instance the inlet pipes p are formed individually and are received in the bores B as part of the manifold 4.

It is an aspect of the present invention that the temperature of the L.P.G. fuel emerging from the nozzle may be utilised^" to determine the constituent mix of the L.P.G. fuel and thus to modify the delivery of the L.P.G. fuel to the engine. In this instance, a temperature measuring device or probe t.p. (see much simplified schematic view of FIGURE 4) is placed in the elongate chamber 20 at the exit of the aperture 13a and informa^*tion regarding the temperature of the L.P.G. exiting the aperture is relayed via line R to an electronics control device E.C.D. which evaluates the information and pulses the solenoid valve of the injector device via line p.s. accordingly to control in a modified manner flow of L.P.G. through the nozzle. The vapourisation temperature of propane at atmospheric pressure is about -40°C and butane vapourises at 0°C and therefore temperature information of the fuel exiting the nozzle 13 can give a direct determination of the constituent mix of the L.P.G. Once the mix has been determined the pulsing of the solenoid can be modified to suit more efficient running of the engine via the electronics control device. Whilst temperature measurement is taking place it is envisaged that the aperture will be fully open without pulsing of the solenoid.

Pulsing of the solenoid may take place by means of a purpose made electronics control device, E.C.D. , which may be arranged to receive input information from various sensors S-_j_, ≤2, S , S₄, S5, such as engine speed sensors, inlet manifold compression sensor, throttle opening sensors, exhaust sensors, air flow and temperature sensors and so on, and which may provide a signal to pulse the solenoid in accordance with pre-programmed information in order to run the engine efficiently. Information from said temperature measuring device or probe t.p. at the exit of aperture 13a acts as an additional override or modification signal to the pulsing signal.

Referring to FIGURE 5, it is a further aspect of the present invention to provide, in a cost effective way, adequate fuel injection, utilising an existing electronics control device A.E.C.D. (and sensor array S₁',S2^,,S3' S₄', S₅') which is already available for internal combustion engines designed to run on other fuels, for example, petrol (either fuel injection or carburettor). In this way, for example, an existing internal combustion engine designed to run on petrol and already including an electronics control device A.E.C.D. and sensor array S--_ ^■ , S₂' , S₃' , S₄', S₅' can be converted to run on L.P.G. by the relatively simple modification of providing the L.P.G. fuel flow control injector device 1 and simplified electronics control device E.C.D.l in the line between device A.E.C.D. and the original fuel injector I. Signals derived from sensor array S_j_' to Sg' and fed to control device A.E.C.D. can, advantageously, still be utilised and modified by the new, additional, control device E.C.D.l to control the pulsing of the solenoid actuated flow control injector device 1, whilst the original fuel injector I can remain intact and operational in the event that the engine is to be run once again on its previous fuel. Thus, it is possible that the engine may be designed to run in a dual-fuel mode. The probe t.p. is optionally provided in this system. In this way a very much more simple and less expensive system is provided to convert an internal combustion engine to run on L.P.G., by the simple integration into the existing control system of a further control device E.C.D.l and additional flow control injector device 1 for L.P.G. Thus the programming and 5 electronics of E.C.D.l can be made much more simple (qualitative use being made of the already extensive programming of the device A.E.C.D. ) and an additional complete range of sensors feeding information thereto is not required in such circumstances. Thus the device

ICC^* E.C.D.l converts existing control signals from device A.E.C.D. into the required pulsing signal for the L.P.G. flow control injector device (or injector devices where applicable), and as stated there is no interference with the existing fuel supply system and control system should

15 it be desired to once again run the engine on its previous fuel. In an alternative arrangement one or more of the sensors S-_j_' to S-*' can be utilised to supply signals directly to control device E.C.D.l in order to control the flow control injector device 1, by bypassing

ZO the original control device A.E.C.D. However, in such a case the control device E.C.D.l may be more complicated than need be.

Additionally, the arrangement could be that, when 25 running on L.P.G. the electronics control device E.C.D.l is arranged to effectively program the existing device A.E.C.D. to provide modified output signals for controlling the L.P.G. injectors. Sensor signals may or may not be fed directly to device E.C.D.l. 30

The original fuel pump will be turned off and as far as the original control device A.E.C.D. is able to evaluate the situation the engine will still appear to be running on its previous fuel, e.g. petrol, so that to all 35 intents and purposes the L.P.G. fuel injector system will mimic the original fuel injector supply. Of course, if desired, additional sensors may be incorporated into the system and such sensors may feed signals directly back to the control device E.C.D.l.

Yet a further aspect of the present invention is concerned with improving efficiency at low engine speed. A device or means equivalent to an injector pump seems essential for immediate acceleration from low engine speed. This is achievable by injecting either liquid or gaseous L.P.G. into the engine. For injection of liquid L.P.G. this can be achieved by programming the control device E.C.D or E.C.D.l to increase momentarily the output of the solenoid valve. However, in order to yield a quicker response it can be preferable that a separate L.P.G. supply to a separate solenoid valve (not shown) is provided. The gas can be fed into the inlet manifold either through the existing L.P.G. injector device(s) or through a separate tapping further upstream in the air inlet manifold which feeds all cylinders. In either case, a signal to inject additional L.P.G. fuel is discerned by the microcomputer of E.C.D. or E.C.D.l from the pressure signal from pressure transducers sensing inlet manifold vacuum. When this pressure rises suddenly, such as when the throttle is suddenly opened, and when this happens below a certain predetermined pressure, the microcomputer assumes the engine is required to accelerate and injects the additional amount of fuel required.

Provision of a separate gas solenoid valve for injecting additional gas for acceleration purposes, may also be used for hot restart conditions when gaseous L.P.G. capable of being passed through the liquid L.P.G. flow control injector device is insufficient to give more than engine idle conditions. When the temperature sensor senses that gaseous L.P.G. is coming from the liquid L.P.G. injector device it not only opens the liquid L.P.G. injector valve fully, of which the opening is inherently small, but it also opens the gas solenoid used for acceleration purposes and feeds in substantially greater amounts of gas. When liquid L.P.G. finally emerges from the injector device and produces a considerable temperature drop, the gas solenoid valve is closed by the microcomputer and the engine operates normally. This will substantially reduce the irritation under hot restart conditions of having to wait for liquid L.P.G. to thread its way right through the system.

The present specification has so far described L.P.G. fuel systems which are especially suitable for being superimposed on petrol fuel injection systems of a known type, such as the so-called Bosch 'L' Jetronic type, in which the fuel is metered by means of solenoid valves which are pulsed at varying pulse widths and frequency. These are now widely used. In some earlier versions of petrol fuel injection systems for petrol fuel injection engines, however, such as the so-called Bosch 'K' Jetronic system, the fuel supply to the injectors is continuous and variation in flow is achieved by altering the supply pressure. The air flow to the engine passes through a large diameter tapered venturi which has a plate of suitable diameter which can completely block it at the smallest diameter of the venturi. The plate is suspended on a pivoted arm and a light spring pressure pushes the lever and thus the plate to its closed position blocking off the venturi. Air flow to the engine moves the plate further up the venturi and the resulting movement of the pivoted arm acts on a petrol metering plunger (biassed by a control pressure) and so regulates the fuel supply to the engine. Thus the air flow to the engine dictates the position of the plate in the venturi which controls the metering of the fuel and thus regulates the fuel supply. Assuming this arrangement is correctly designed, the engine is then supplied with fuel to give stoichiometric operation over its entire operating range. In this connection reference is directed to the annotated diagrams, labelled FIGURES 6 and 7 of the drawings, illustrating a typical Bosch 'K' Jetronic fuel injection system.

The inventor has found that engines fitted with the above-mentioned 'K' Jetronic type fuel system can readily be adapted to accommodate an L.P.G. fuel system, e.g. of the kind as aforementioned, and can still utilise the aforesaid pivoted arm and plate device as a sensor simply by adding an electronic device to sense the position of the pivot arm, the position of which when in use is a function of fuel required by the engine. A signal from this "positionometer" is then fed to the electronic control unit or "black box" which regulates the L.P.G supplied, for example by altering the pulse width and/or frequency of the L.P.G flow control injector device.

In this arrangement, the said L.P.G injector device may be in a housing identical to the one as previously described. The sensor or positionometer could be of several different types, such as for example an inductive positionometer or a sliding linear potentionometer or sliding rheostat, and it can be placed in several selectable positions to measure the movement of the pivot arm.

It. may be noted that since the petrol metering plunger has a control pressure on top of it the resulting force opposes the force generated by the air flow past the metering plate. The said control pressure is a function of engine temperature inlet manifold vacuum and is used to weaken the mixture at cruise, to give slightly richer mixture at full throttle for maximum power and to give a much richer mixture when starting from cold. There is also an air bleed for cold starting to ensure the engine idles when cold despite the increased resistance due to thick oil. All of these features are inherently taken care of by measuring the position of the metering arm. Although it will still generally be necessary to measure the L.P.G supply pressure to the L.P.G flow control injector device since in both systems this clearly has a substantial effect on the fuel supplied, this can be taken care of by means of a "look¬ up" "table in the programme which uses historic data.

Therefore, further according to the present invention there is provided apparatus comprising an L.P.G. fuel flow control injector device and an electronics control device utilisable: in conjunction with an existing sensor used to supply information to control the running of an internal combustion engine designed to run on a fuel other than L.P.G., for example petrol or diesel, said apparatus being able by way of said utilisation to control the injection of L.P.G. into an internal combustion engine in accordance with engine requirements.

Further according to the present invention" there is provided a method of injecting L.P.G. into an internal combustion engine comprising utilising: control signals from an existing sensor in or for an internal combustion engine designed to run on a fuel other than L.P.G. (usually petrol), in order to regulate the supply of L.P.G. through an L.P.G. injector device into said engine.

Preferably, by way of this aspect of the present invention the original fuel supply system (usually fuel injection) will be undisturbed so that if desired the engine could be run on its original fuel by way of the original electronics control. Still further according to the present invention there is provided a dual fuel internal combustion engine adapted to operate in a first mode as a petrol injection engine utilising petrol as a fuel injected in metered quantities by petrol injection devices controlled (usually in accordance with established technology) by first control means responsive to one or more sensors arranged to sense various engine conditions or requirements during operation, wherein the engine is also adapted to operate in an alternative mode utilising L.P.G. as a fuel injected into the air intake by an L.P.G. metering injector device or devices controlled by electronic control means arranged to respond to the same said sensor or sensors that, in said first mode, are used to vary the flow of petrol to the engine.

The inventor has found that where the injector device is solenoid actuated, it is most preferably a plate-type fuel injector (e.g. a Lucas petrol injector) rather than a Bosch type injector. In the arrangement as shown in FIGURE 1 such a plate-type fuel injector works well due to the pressure balancing of the device.

In practice, one injector device housing assembly is preferably utilised for every two cylinders of the engine (therefore two pipes p are provided rather than the four pipes p as shown) since this, advantageously, allows the length of tubing T (not shown except in FIGURE 10) from pipes p to the inlet manifold (see FIGURE 10) of the engine to be relatively short. The length of tubing T to the inlet manifold can affect the throttle response and, therefore, should be kept relatively short although it needs to be long enough to allow proper mixing of the L.P.G. with air before entering the engine cylinder. Under certain operating conditions e.g. at low speed, when the throttle is released a vacuum may build up in the pipes p or tubing T which can cause some time delay in throttle response as soon as the throttle pedal is again depressed (since the vacuum creates a small time lag in the supply of liquid fuel until it is removed by the fuel being fed through the system).

By using one such injector assembly for every two cylinders (or in an alternative arrangement for every cylinder) the size of the injector assembly can also be made, advantageously, of a smaller size (in addition to the tubing being shorter). Throttle response is thereby improved and it is also easier to fit smaller injector assemblies into the confined space available around the engine.

The tubing T may be small bore nylon pipe (1.5 mm) which will still allow the engine to run at full power and the throttle response at low speeds is good even though a vacuum may occur in the tubing on overrun as a orementioned. Nevertheless, it is possible to increase the throttle response still further by the elimination of such a vacuum in a manner which is described later on in the specification (with reference to FIGURES 8 and-10).

Where a petrol engine is adapted to run on L.P.G. and the signal output of the existing electronics control device A.E.C.D. is modified when running on L.P.G. to control the fuel flow control injector device in the manner previously described, certain sensors used in running the engine are generally not required. Thus, the usual cold-start or exhaust sensor signal is not normally required and also the usual petrol addition (fuel enrichment) sensor is not required when running on L.P.G.

The present invention thus provides:-^*

(1) Use of petrol injection sensors to give signals to an L.P.G. fuel control computer. This eliminates the cost and fitting time of an L.P.G. system having its own sensors. This method is needed for continuous petrol injection systems like the Bosch 'K' Jetronic.

(2) When running on L.P.G, the system may effectively mislead the petrol injection control computer into behaving as if it is still running on petrol. The resulting pulse width it generates for the petrol injectors is intercepted and modified for, for instance, varying tank L.P.G temperature and hence pressure, and is fed to the L.P.G flow control injector device or devices instead. It may be necessary to eliminate some of the signals fed to the petrol computer, however, and the following should be noted:

(a) An engine temperature signal is usually provided to cause fuel enrichment when the engine is cold. This may be unnecessary or even detrimental when running on L.P.G;

(b) There is usually provided fuel enrichment _ with petrol as the fuel when the throttle is wide open to give maximum power. This enrichment is far greater than is needed when running on L.P.G., there being no commensurate increase in power for a substantial increase in L.P.G. consumption which also gives inferior exhaust emissions. This differentiation between operation on petrol and on L.P.G. can be achieved by a dummy jack plug between the existing jack plug on the end of the usual wiring loom feeding the petrol control microcomputer and the L.P.G. control computer. The separate signals are passed to the L.P.G. computer and are interfered with or not as required. In the design of such systems which run on L.P.G. a further problem exists which has not yet been fully discussed. The problem is the "Hot re-start" problem. When the engine is not in operation and has been standing for some time in a hot environment the fuel supply system becomes full of gaseous ^" L.P.G. , e.g. when the engine compartment and gas feed pipes are hot from standing in the hot sun for instance, the pipework from the tank and the L.P.G. flow controller (injector) are full of gaseous L.P.G. This gives rise to problems in starting the engine.

To meet this problem, the inventor provides a sensor which is fitted just before (after would also probably be satisfactory) the L.P.G flow control injector. This sensor consists of a resistance (platinum wire resistance, for example) through which a small pulsating current (m.amp) is passed at constant voltage. The current which flows is a function of the resistance of the wire and hence of its temperature. When the resistance is submerged in liquid, the temperature rise is very small. When it is in gas, the rise is much higher. When it is in a froth (L.P.G gas _andT^"l_iquid mixture), the temperature rise is somewhere inbetween. By careful calibration, the sensor gives a signal of whether the injector device is being fed with gas, liquid or froth L.P.G. From -laboratory calibration, the pulse width of the solenoid operated injector can be varied so as to give the appropriate energy supply to the engine for a given condition whether the injector is fed with liquid, gaseous or froth L.P.G. This results in the ability of the system to restart the engine after a 'hot soak' . The engine runs- on gaseous L.P.G until the liquid L.P.G, feeding through from the tank and cooling the pipework on the way by boiling thereof, is available at the injector. Once the liquid has reached the injector, the pulse width reverts to that required for metering liquid L.P.G. The process takes only a few seconds (5 to 10 seconds) under worst conditions before liquid L.P.G. operation is available. Thus, the vehicle can drive off after a hot soak.

If the pulse width of the injector device is increased, for instance to a ratio value 3.7/1 the engine runs quite successfully on gaseous L.P.G with the injector effectively metering gaseous rather than liquid L.P.G. Thus, the present invention also provides a system for varying the pulse width of the flow control injector under hot re-start conditions in accordance with requirements.

Another advantage of the system as described in general terms which keeps the L.P.G. in a liquid form up to the injection is that 'rubbish' in the L.P.G. such as water, rust particles, heavy ends etc. pass straight through the engine and harmlessly down the exhaust pipe. They do not collect in the vaporiser and cause malfunction as on a conventional system.

The system also eliminates the need for a mixer as used on a conventional L.P.G. system, i.e. a venturi in the air supply to the engine which creates a depression that is a function of air flow and results in a gas L.P.G. supply hopefully proportional to air flow. However, said depression interferes with the operation on petrol. Thus, an engine pronounced 'clean' for emission control purposes on petrol is not 'clean' after a conventional L.P.G. gas conversion. This can result in severe financial . penalties in some countries (like Holland). Advantageously, the system in accordance with the present invention does not interfere with the operation on petrol.

Also, advantageously, by feeding liquid L.P.G. into the inlet manifold, the boiling of the liquid L.P.G. to gas L.P.G. takes place in the charge air, thereby cooling the latter and increasing the power output available due to the increased charge density.

By using an injector submerged in L.P.G, the injector is pressure balanced and can so withstand enormous L.P.G pressures used for approval purposes which the injector would not otherwise withstand. This enables a standard petrol injector body to be used which is mass produced and available much more cheaply than a purpose built injector would cost.

By cooling the fuel to ensure that it is liquid at the L.P.G. injector, so ensuring accurate metering under normal conditions, the need for a fuel pump which may be expensive, noisy, unreliable, and have high current comsumption is eliminated. By using the boiling fuel after it has been metered to cool the incoming L.P.G. via the heat exchanger, the use of a heat pump, either mechanical or electrical, with high current comsumption and cost is eliminated.

By having a constant pressure drop across the L.P.G. flow controller, a temperature drop will occur due to the boiling that takes place. By measuring the temperature drop using a temperature sensor upstream and downstream of the flow controller, caused by this pressure drop, an assessment of the composition of the L.P.G. can be made i.e. pure propane, butane, or mixtures thereof. This information, fed to the computer, can correct accordingly for the different calorific heat values of the differing fuels supplied.

As aforementioned, the present invention may provide a system in which the occurrence of a vacuum in the tubing from pipes p is substantially eliminated. The present invention, therefore, provides that a mixer screwed or otherwise fitted into the air inlet manifold may consist of a fuel inlet spring loaded ball valve which is fed with a signal of gas tank pressure. The ball valve opens when the supply pressure from the flow controller is a fixed amount less than tank pressure, typically half a bar. The advantage of this device is two fold:-

(a) the pressure drop across the L.P.G. flow controller (injector) is maintained at a constant pressure (half a bar) and this eliminates the need to correct for tank pressure variation with temperature. This simplifies the algorithim in the computer. More importantly, it eliminates the need for a pressure transducer, a major cost item.

(b) the pipe from the flow controller to the mixer is normally full of liquid L.P.G. due to the back pressure caused. This improves throttle response because as soon as there is a variation in the flow at the flow controller, the same variation takes place at the mixer since there is generally liquid in the connecting pipe. Furthermore, on the overun, the gas supply from the mixer stops immediately and the connecting pipe does not empty. This normally causes a very rich slug of emissions when the throttle is shut and the connecting pipe empties. Furthermore, when the throttle is reopened, the pipe is already full of fuel and again response time is greatly enhanced.

An example of an L.P.G. fuel inlet valve located in the tubing T (see FIGURE 10) from a respective pipe p to the inlet manifold to prevent vacuum formation in the tubing as aforesaid, will now be discussed in relation to FIGURE 8 of the accompanying drawings which shows a cut¬ away perspective view of the valve. FIGURE 10 shows a much simplified overview of the engine fitted with an L.P.G. fuel control system, as described.

The L.P.G. fuel inlet valve as shown in FIGURE 8 consists of three housing H^, H₂, H3, located to each other by spigots and held together with four screws. Conveniently, they may be die cast in aluminium alloy or injection moulded from plastics..

The top housing H_]_ contains a chamber C_j_ which is fed with pressure directly from the L.P.G. fuel tank. Trapped between this chamber C-_j_ and the middle one C₂ is a diaphragm D. The diaphragm D seals the chamber C₂ which is fed with fuel directly from the L.P.G. flow controller (injector). Touching the diaphragm D is a valve seat V.S. which is spring loaded in the open direction. The mating part of the valve seat is screwed into the bottom housing in such a way as to be adjustable. This ensures that in production the assemblies can be individually adjusted to ensure they each give identical performance.

When the L.P.G. system is switched on, but there is no fuel demand, i.e. when the engine is stationary or on overrun, the tank pressure on the diaphragm D is sufficient to overcome the spring force and close the valve. There is thus no fuel supply to the engine which ensures that the L.P.G. feed pipe from the L.P.G. controller to the fuel inlet valve remains substantially full of liquid. When engine conditions require a fuel supply, i.e. normal operation, the flow controller passes L.P.G. fuel, which opens the valve in the inlet valve and feeds the engine through the inlet manifold (see FIGURE 10). The L.P.G. fuel mixer which incorporates the valve face, protrudes slightly into the air stream in the inlet manifold. The L.P.G. fuel is directed through two small holes preferably facing upstream such as to spray the fuel at an angle of approximately 45° either side of the centreline of the air flow. This has been found in practice to give excellent mixing of the fuel with the engine charge air.

The advantages of this arrangement are twofold. Firstly, the pressure drop across the flow controller (injector device) remains constant regardless of tank pressure so eliminating the need for a pressure transducer, a major cost item. Secondly, the fuel pipe from the controller to the inlet valve remains substantially full of liquid fuel when the fuel supply is temporarily closed. When the supply reopens, the response time is nearly immediate since the line is full of liquid and does not need time to fill up. Furthermore, on the overrun, with the fuel supply shut off, the fuel contained in the pipe from the flow controller to the fuel mixer does not discharge into the engine creating bad exhaust emissions and wasting fuel.

The L.P.G. fuel control system has already been discussed in relation to FIGURES 4 and 5 and further possibilities are now discussed in relation to FIGURE 9.

The L.P.G. fuel control system shown in FIGURE 9 is based on a microcontroller device which incorporates integral analogue to digital converter and high speed digital timing units which are used as follows:

When the gas/petrol selector switch is in the gas position the petrol injection control system is powered up as normal, but the petrol pump is switched off and the petrol injector drive signal is removed from the injectors and routed to the L.P.G. control system. In addition the engine temperature signal to the petrol injection system is modified and the full throttle enrichment switch is disabled. The effects of these actions are:

i) the supply of petrol to the engine is stopped; ii) the L.P.G. control system is provided with a signal of engine speed and petrol fuelling requirements; iii) over fuelling under cold engine conditions is prevented; the excess fuelling required with petrol under cold conditions is not required with L.P.G; iv) the full throttle enrichment provided on the petrol system is disabled to allow this function to be performed more smoothly and accurately by the L.P.G. control system.

The microcontroller in the L.P.G. control system is now able to control the flow of L.P.G. to the engine in the following manner.

The injector drive signal from the petrol injection control system is monitored by the microcontroller high speed input system which measures both the frequency of the drive pulses from which is derived the engine speed signal, and the duration of the injector drive pulse which is used in conjunction with the battery voltage level to determine the required fuelling level. Under transient conditions the rate of change of the fuelling signal together with the engine speed is used to modify the fuelling requirement to provide any required acceleration enrichment. From the signals of engine speed and petrol fuelling requirement the microcontroller can then determine from a table of pre-programmed engine specific parameters the quantity of L.P.G. required and provides this by programming its high speed output section to accurately control the frequency and width of the pulses used to drive the L.P.G. flow controller. This is done in conjunction with the signal from the gas/liquid sensor incorporated within the gas flow controller unit to ensure that whether gas or liquid is being metered the unit is driven in such a way as to ensure that the required fuel energy flow is achieved. The flow controller drive is also modified to permit fuelling to cease under over-run conditions and when the engine is stationary.

The microcontroller also preferably incorporates a serial communication link which is used to connect an external programming and diagnostic unit which is used to initially program the system with all the parameters required to tailor the system to the engine to which it is fitted, to perform any adjustments required and to provide diagnostic information.

The above description is only one embodiment of the system which allows the benefits of refinements to the petrol injection system such as exhaust emission control to be used by the L.P.G. system. The system may however be implemented such that the existing petrol inj ction system is not used, but signals are taken from the existing sensors e.g. the air flow meter either directly or indirectly using electro-mechanical transducers to enable the system to operate on non-electronic petrol systems.

The performance of the system may also be improved by using the high speed input/output section of the microcontroller to modify the ignition timing characteristics to suit the fuel being used. The microcontroller also has the capacity to measure the fuel tank pressure and temperature which may be used to provide a measure of compensation for different L.P.G. compositions which may be encountered.

It is to be understood that the scope of the present invention is not to be unduly limited by the particular choice of terminology and that a specific term may be replaced by any equivalent or generic term where sensible. Further it is to be understood that individual features, method or functions related to the fuel ' injection and/or electronics control or combinations thereof- might be individually patentably inventive. Additionally, the present invention may encompass an engine including one or more fuel injectors and one or more electronic control devices. The present invention may encompass equipment for fitting to an existing engine designed originally to run on a fuel other than L.P.G. (for example petrol) and may be part of an engine which is specifically designed to run on L.P.G., with or without *being provided with an alternative fuel supply system. The electronics control device itself may be individually patentably inventive. The fuel flow control injector itself may be individually patentably inventive.

The electronics control device and/or sensor array usually utilised, for example, for a petrol engine may comprise part of original equipment (with the additional electronics control device) to be fitted to an internal combustion engine to run on L.P.G.

Further it is also possible that, in certain instances, the present invention may be utilised with fuels, other^*than L.P.G. such as other "liquefied gaseous fuels" and reference is made in full to patent application No. GB 2014336A having an inventor in common with this application.

Claims

1. A dual fuel internal combustion engine adapted to operate in a first mode as a petrol injection engine utilising petrol as a fuel injected in metered quantities by a petrol injection device or devices controlled by first control means responsive to one or more sensors arranged to sense various engine conditions or requirements during operation, wherein the engine is also adapted to operate in an alternative mode utilising L.P.G. as a fuel injected into the air intake by an L.P.G. flow control injector device or devices controlled by electronic control means arranged to respond to the same said sensor or sensors that, in said first mode, are used to vary the flow of petrol to the engine.

2. An engine as claimed in Claim 1 in which in said L.P.G. injector device or devices a temperature measuring device or probe is located, in use, preferably adjacent an exit aperture of a nozzle of the associated fuel injector device, said measuring device or probe being arranged to sense the vapourising temperature of L.P.G. liquid exiting said aperture and to relay temperature information to a control device to regulate the supply of L.P.G. via said injector device accordingly.

3. An engine as claimed in Claim 2 in which the control device is the electronics control means.

4. An engine as claimed in any one of the preceding claims in which the injector device is solenoid actuated.

5. An engine as claimed in any one of the preceding claims in which the L.P.G. fuel is pre-cooled before exiting.the injector device or devices.^'

6. An engine as claimed in any one of the preceding claims in which the first-mentioned control means is electronic and in which the second electronic control means is arranged to respond to signals from the first electronic control means.

7. An engine as claimed in any one of the preceding claims having a sensor arranged to detect the L.P.G. status (i.e. liquid, gas or froth status), said sensor being located adjacent to said injector device and being able to supply a signal indicative of said L.P.G. status to the electronic control means to control the opening response of the injector device.

8. An engine as claimed in any one of the preceding claims in which the occurrence of a vacuum in tubing from said injector device to an inlet manifold of the engine is eliminated by automatically operable valve means, preferably, by a spring-loaded ball valve.

9/ An engine as claimed in Claim 8 wherein operation of said valve means is controlled by differences in the pressure in the L.P.G. supply upstream and downstream of the flow control injector device or devices.

10. A method of injecting L.P.G. into a dual fuel internal combustion engine comprising utilising: control signals from existing sensor means in or for an internal combustion engine designed to run on a fuel other than L.P.G. (usually petrol), in order to regulate the supply of L.P.G. through an L.P.G. injector device into said engine.

11. A method as claimed in Claim 10 and of controlling or modifying the regulation of L.P.G. supply to said internal combustion engine from said L.P.G. injector device or devices depending upon the proportion of at least some of the constituent parts (normally the proportion of propane to butane) of the L.P.G. mix, said method comprising:-

sensing the temperature of vapourisation of the L.P.G. and relaying temperature information to a control device for issuing control signals to regulate the supply of L.P.G. from the injector device.

12. In a dual fuel internal combustion engine, apparatus comprising an L.P.G. fuel injector device and an electronics control device utilisable: in conjunction with a sensor used to supply information to control the running of an internal combustion engine designed to run on a fuel other than L.P.G., for example petrol or diesel, said apparatus being able by way of said utilisation to control the injection of L.P.G. into said internal combustion engine in accordance with engine requirements.