FUEL SUPPLY SYSTEM FOR INTERNAL COMBUSTION ENGINES

Abstract: A liquefied petroleum gas supply system for an internal combustion engine, consisting of an electronic control unit (17) which controls the operation of an injector (14) to inject liquefied petroleum gas in the liquid state into an inlet airstream to the engine (15), an air flow-rate transducer (16) which provides an electrical signal to the control unit in accordance with the magnitude of the airstream flow-rate, and means to provide an electric signal indicative of engine speed to the control unit, the control unit operating the injector and thus controlling the amount of liquefied petroleum gas supplied to the engine. Further inputs to the control unit may be provided from thermistors (114, 116) located to provide an indication of liquefied petroleum gas temperature at the gas container (10) and at the injector (14), and from a pressure transducer (128) responsive to manifold pressure, to enable the injector operation to be controlled more accurately in relation to the further fuel and engine parameters.

Description: FUEL SUPPLY SYSTEM FOR INTERNAL COMBUSTION ENGINES This invention relates to fuel supply arrangements for internal combustion engines, and in particular relates to a fuel supply system for operating an internal combustion engine on liquefied petroleum gas (LPG) . The invention has particular utility in the conversion of such engines from operating on petrol to operating on LPG, either solely, or as a dual fuel system whereby one or the other fuel may be selected by operation of a suitable control. Systems for converting internal combustion engines from operation on petrol to operation on LPG either singularly or as a dual system are well known, and with the increasing cost of petrol, conversion to LPG has become extremely popular, particularly in the automobile field. Existing conversion systems however, suffer a number of disadvantages; the main disadvantage is the relatively high cost of conversion which can only be justified on a cost basis if the annual distance travelled by a vehicle is extremely high, as is the case with commercial vehicles. The high cost evolves from the high cost of components as well as the high installation costs brought about partly by the time involved in tuning the engine once installation is completed. Thus with installation costs around A$750.00 the time to recoup the investment is too great to justify conversion on a cost basis in many cases. The relatively high cost of components in known systems is brought about by the number of components whi comprise a gas bottle, lock-out valve and filter, heated pressure convertor/vaporiser and mixer in the form of a special carburettor or a mounting adapted to fit on top of the existing carburettor for dual fuel systems. The pressure convertor reduces the liquid pressure of about 689 to 1379 KPa from the tank to a gas pressure of about 34 to 76 KPa. The convertor is required to be heated to prevent freezing and this considerably increases the complexity of the installation and hence the cost thereo Further disadvantages of existing systems resul from the fact that the density of gas cannot be easily controlled so as to eliminate excessively high temperatu during combustion and hence stellite valves and valve seats are necessary in many cases otherwise burnt-out valves result. Also, once the air/fuel ratio is set during the tuning operation it remains fixed and cannot alter during varying engine conditions such as during acceleration when fuel enrichment is required. A still further disadvantage in the way of safety can occur if th low pressure hose bursts since the low pressure disrupti may not be sufficient to activate a safety valve at the pressure vessel (gas bottle) . Thus it is an object of this invention to provi an improved LPG supply system for an internal combustion engine, which system avoids or at least reduces one or more of the aforementioned disadvantages. Accordingly one broad form of the invention provides a liquefied petroleum gas supply system for an internal combustion engine, characterized in that inject means (14) are provided to receive high pressure liquefi petroleum gas fuel, in the liquid state, from a fuel storage container (10) , and, when operated, to inject sa _ . OMP fuel, in the liquid state, into an inlet airstream to said engine (15) , and in that electronic control means (17) adapted to receive a first electrical signal indicative of an engine parameter, and a second electrical signal indicative of the air flow-rate in said airstream, control the operation of said injector means, in response to said first and second electrical signals, such that said injector means is operated for a given period of time during each engine cycle, depending on the magnitude of the air flow-rate and the engine parameter. Preferably said system includes means to maintain the LPG behind said injector in a liquid state. In order that the invention may be more readily understood embodiments thereof will be described in detail hereinafter, with reference to the accompanying drawings, wherein, Fig. 1 is a simplified block diagram showing the components of a first embodiment of system according to the invention; Fig. 2 is a schematic diagram of the injector and air flow-rate transducer of the system according to Fig. 1; Fig. 3 is a circuit block diagram of the electronic control circuitry of the system according to Fig. 1; Fig. 4 shows various pulse trains occurring in the circuit diagram of Fig. 3; .. Fig. 5 is a simplified block diagram showing the components of a second embodiment of the system of the invention; and Fig. 6 is a circuit block diagram of the electronic control means of the system according to Fig. 5. Referring now to Fig. 1 there is shown a fuel tank O PI (gas bottle) 10 connected via a high pressure line 13 to one or more fuel injectors 14. A lock-out valve 12, whic with the gas bottle 10 are conventional units used in LPG systems for motor vehicles, is located in line 13 between bottle 10 and injectors 14. At the fuel injectors 14, high pressure liquid gas will be injected in the liquid state into the intake airstream to a motor 15, wherein it • will convert to vapour. A transducer 16 is arranged in the inlet airstream to .measure the air flow-rate thereof and provide an. electrical signal related to the air flow- rate. The electrical signal is connected to electronic control circuitry 17 which also receives a further electrical signal from the motor 15 indicative of engine speed- and in response to the two electrical input signals provides .an output pulse train to the or each injector. Referring now to Fig. 2, there is shown a conversion unit for attachment to the mouth piece or air intake end of an engine air cleaner 18. The diagram is only schematic and therefore it does not show the means for attaching an inlet type 19 of the unit, to the air cleaner 18 but conceivably this could be done merely by cutting away the flared end of the air cleaner 18 and sliding the inlet pipe 19 thereover where it could be hel by a suitable clamp (not shown) . The air flow-rate transducer 16 is mounted in the inlet pipe 19 and, according to this embodiment, comprises a flap which is moved by the airstream in relation to the flow-rate, and is connected to a transducer element 20 so as to generate an electrical signal at varying strengths dependent upon the air flow-rate. The transducer 16 is adapted to provide a voltage output which is thus related to the air flow-rate and the voltage output is connected via connection 21 to the electronic control unit 17. The unit 17 receives from the engine, on connection 22, an electrical signal from either the OMP < primary or secondary ignition pulses, and this signal is indicative of engine speed. As an optional feature the circuitry 17 may also receive on connection 23 a further electrical signal from a pressure transducer (not shown) connected to the manifold vacuum pressure. This further Optional signal may be used to provide fuel enrichment during periods of heavy acceleration where extra fuel is required initially in order to avoid a lag in engine response time. The electronic injector 14 is mounted in the side of inlet pipe 19, elsewhere in an air filter arrangement, or in any other engine inlet airstream. The injector 14 may be a conventional petrol injector for an internal combustion engine, although it is possible that specially designed injectors may be used. Although only a single injector is shown in Fig. 2 there may be according to this embodiment, two or more separate injectors connected to the inlet pipe 19, air filter, or the like. The high pressure line 13 feeds high pressure gas in liquid form into the injector, and opening of the injector according to electronic pulses on connection 24 causes the liquid.gas to be ejected therefrom; which . changes into the vapour state in the inlet airstream. The arrangement of the injector 14 with relation to the direction of air flow causes the vapour to be ejected at least across the inlet airstream and this has the effect of creating further turbulence which ensures a good mixing between the vapour and the inlet air. This mixing is further enhanced by the fact that the injection takes place well upstream from the motor thus enabling more adequate mixing to occur in the course of transmission of the air¬ stream through the inlet manifold and cylinder head ports. Reference should now be made to Fig. 3 which is a circuit block diagram of the electronic control circuitry 17. The control circuitry 17 includes a multivibrator 25 OMFI < ° which generates a square wave pulse signal at a preset frequency (see wave form A in Fig. 4) . The square wave signal from multivibrator 25 is provided to pulse width control circuitry 26 1, 262 and so on, which provides respective pulse trains at the multivibrator frequency but separated by half a period of the pulse train A. Th pulse width of the pulses from the pulse width control circuitry 26 1, 262 is controlled by a signal from pulse width generator 27 which generates a pulse dependent upo air flow-rate as .determined by the transducer 16. Input pulses from ignition coil 118 operate to allow the pulse width controls 26 1, 262 — 26N to operate. The output from the pulse width control circuitry 26 1, 262 — 26N i amplified by respective driver/amplifiers 28 , 28 — 28 which provide suitable outputs to drive the respective T *__) electric injectors 14 , 14 — 14 . The air flow-rate transducer 16 provides a voltage proportional to the air flow-rate. This voltage is then adjusted via the pulse width generator 27 to giv a control voltage which will control both pulse width control circuitry 26 and 26a. Thus for different air flow-rates, (and for fuel parameters.,; for example., fuel container temperature,; if desired.). there are different injector opening times which provide the correct air fu ratio. If the engine ceases to operate this condition is detected by control circuitry 26 and 26a which switch off the injectors 14 and thus prevents gas from flowing to the.engine. In other words, at any time when there are no ignition pulses the supply of gas is switched of and thus a dangerous situation is avoided. The dotted lines in Fig. 3 show N injectors 14 1 — 14N, with associated control circuitry. In Fig. 4, as mentioned above, the pulse train represents the pulse train from the multivibrator 25. OM Pulse train B represents the resultant pulse train to the injector number 1 and pulse train C represents the resultant pulse train to injector number 2. Pulse train D is the sum of the pulse trains B and C and represents the total injector 'on' time considering both the injectors 14. The conditions represented by pulse trains B and C are for slow operation of the engine, such as during idling conditions. Pulse trains E and F show respective pulse trains for injectors number 1 and number 2 during fast engine running conditions such as during full throttle conditions when the engine has reached maximum speed. Operation of the system should be evident from the above description. Briefly the operation is as follows. When the ignition.is switched "on" the lock-out valve 12 is allowed to open and gas in liquid form flows to the injectors. The injectors remain closed until the motor is cranked whereby the injectors are opened for a limited time (approximately 2 seconds for an average six cylinder engine) . If the motor starts the injectors will operate via the electronic control circuitry to give the right air fuel ratio. If the motor fails to start the injectors will switch off. When the injectors are in the open condition the gas rushes out and vaporises almost instantaneously, thus mixing with the air entering the motor. Thus it is not necessary to have a converter/ vaporiser as with conventional systems. The injectors used in the above embodiment are of the "on-off" type but variable injectors capable of various positions between the "on" and "off" condition may be used. The embodiment of Figs. 5 and 6 includes a mechanism which ensures that the LPG gas remains in liquid form in the line behind the injector. Most of the features shown in Figs. 5 and 6 are common with those in the OMPI - 8 - embodiment of Figs. 1 and 2, and are denoted by the same reference numerals. A filter 136 may be located in line 13 af er tank 10. In this embodiment, there is a subsidiary line 100 branching from main line 13. The flow of liquid LPG gas in the line is controlled by a second lock valve 102, and the branch line 100 ends in a nipple 104, which, when the lock valve 102 is open, allows liquid to flow into a jacket 106 which surrounds line 13. The liquid passing through nipple 104 vapourizes and expands, absorbing heat from the liquid fuel in line 13. This process, carried o in a controlled manner to be described hereinafter, in the maintenance of a temperature in the liquid LPG gas which ensures that the fuel remains in a liquid state. A gas line 108 bleeds off the low pressure LPG gas from jacket 106 and feeds it to the engine air inlet in a manner to be described hereinafter. Alternatively or additionally a gas line 110 may bleed gas from jacket 106 to be liquefied to a pressure greater than the pressure in tank 10 b a pump 112, and fed back into line 13. An alternative line cooling system envisages a bleeder line to bleed gas, which may develop behind the injector 14, to jacket 106 to act in the same cooling capacity as described in the preceding two paragraphs. Thermistors 114, 116 are provided at the fuel tank 10 and at the main lock valve 12, and are connected to control unit 17. In describing the operation of the Fig. 5 arrangement, in the context of a vehicle internal- combustion engine, the sequence of starting the engine 15 and thereafter supplying fuel thereto is as follows. The ignition control is turned to the on positio and electrical power is supplied to control unit 17, coil 118 and distributor 120. The ingition control is then turned to 'start*. A pulse is generated by the engine movement due to the starter motor actuation, and the pulse is fed to control unit 17, which opens the lock valves 12 and 102, enabling the cooling operation described hereinbefore to take place, maintaining the LPG in.the liquid state in line 13. If the temperature sensed by the thermistor 116 falls below a predetermined valve, the control unit 17 will shut lock valve 102. The thermistors 114, 116 supply temperature information to control unit 17.to enable the injection delivery of LPG to be. properly controlled. The control unit is adapted, at the 'ignition start' sequence, to allow the injector to stay open for a predetermined time (for example 1 to 3 seconds) to allow extra fuel delivery for" engine starting. Once the motor, is running, the air flow-rate transducer 16 provides signals to the control unit 17, and the control unit is thereafter able to control the injector operation having regard to the signals received from the various data input devices. If the ingition system fails for any reason, the control unit has a fail¬ safe mode which acts to close lock valves 12 and 102. As the low pressure LPG in line 108 is fed to the engine inlet, and as that (usually small) additional amount of fuel may affect engine running, a thermistor or other device responsive to the amount or rate of gas flow, or pressure or temperature of the gas, may be located at line 108 and the signals fed to control unit 17, so that the control unit may further adjust the injector operation to compensate for the extra fuel in the form of the low pressure gas. The injector 14 is shown as being located adjacent an engine inlet after air filter 122 and air flow-rate transducer 16, but before throttle valve 124 and throttle switch 126, but it may be located after thos elements. Another modification of the fuel supply system may be a pressure transducer 128 to respond to manifold pressure conveyed by a hose 152 to react to manifold induction pressure, as an alternative to the flow-rate transducer 16 or as mentioned earlier, to provide greater fuel supply for engine starting. In addition, more than one injector may be used; for.a six-cylinder engine, it may be convenient to provide three injectors 130, 132 and 134. Fig. 6 shows a simplified block diagram of features of the control unit 17 of Fig. 5, the control unit being within the designated border. All features common with Figs. 1, 2 and 5 bear the same reference numerals. The control unit .17 includes a regulator 142, multivibrator 138, -air-flow transducer input 140, and power amplifier 144 for operating injector 14. It also includes an ignition control 148 which will actuate lock¬ out valve controls 146, 150 if the engine 15 does not sta It can be seen that thermistor 116 is connected to control 146 to separately control the lock valve 102, and that thermistor 114 is connected into the multivibrat unit 138. Connection from the engine parameter transduce is not shown. It should be evident from the above that the present invention provides a gas conversion system which has considerable advantage over existing systems. The main advantage stems from the fact that a converter/ vaporiser is not required and thus the cost of the system and the installation costs involved therewith are considerably reduced. As the injector/s are arranged t - ■ " N &-. directly in the inlet airstream to the motor there is no problem of freezing occurring as with conventional converter/vaporiser units. The airstream together with the heat from the engine ensures against freezing and thus avoids the need for separate heating such as water heating used in conventional systems. Another advantage is that, when liquid is injected into the airstream it • will lower the temperature of the air-fuel mixture. Thus a more dense mixture enters the combustion chamber giving more power. Furthermore, since the unit of the described system may be connected directly into the air cleaner installation, costs are considerably reduced and the existing carburettor can remain for use in a dual fuel application. In regard to a dual fuel situation it is necessary to provide conventional changeover arrangement to prevent both fuels from being used at the same time. The present invention also provides a system which has advantages in the area of safety over conventional systems, this stems from the fact that the system operates on at least two sources of control - ingition pulses and air flow - and if the ignition fails the injector is "off". Furthermore, since almost all automobiles will be able to use an identical unit, the manufacturing costs are considerably reduced since the number of different components is kept to a minimum. It is conceivable that the conversion system of the present invention could be readily fitted to automobiles having conventional petrol injection fuel supply systems. It should be also evident that the invention is not limited to the particular embodiment described above as many variations thereto could be readily effected. For example, the number of fuel injectors can vary as has been mentioned above and furthermore the location of the OMPl injectors in the inlet airstream can also be varied. Whilst it is preferable that the injectors be arranged as far upstream as possible in the inlet airstream this is not essential and they could be located further down- stream provided suitable mixing can occur. Also whilst the injectors are inclined to the direction of air flow so as to inject gas against the incoming airstream this is merely a preferment and is not essential to the invention. It will be further evident that other types of air flow transducers could be used and in this regard a thermistor or a venturi tube arrangement is conceivable The same system (as described) may also be used if there is only high pressure vapour (at gas bottle pressure) behind the injector, the only difference being that lock out valve 102 does not operate, and the electro control unit is adjusted accordingly. This system can also operate with different gas mixtures. Present gas conversion units need a minimum amount of propane to operate. The unit described will operate at different amounts and different gases mixtures in liquid form. O

Claims: - 13 - 1. A liquefied petroleum gas supply system for an internal combustion engine, characterized in that injector means (14) are provided to receive high pressure liquefied petroleum gas fuel, in the liquid state, from a fuel storage container (10) , and, when operated, to inject said fuel, in the liquid state, into an inlet airstream to said engine. (15), and in that electronic control means (17) adapted to receive a first electrical signal indicative of an engine parameter, and a second electrical signal indicative of the air flow-rate in said airstream, control the operation of said injector means, in response to said first and second electrical signals, such that said injector means is operated for a given period of time during each engine cycle, depending on the magnitude of the air flow-rate and the engine parameter. 2. A liquefied petroleum gas supply system as defined in claim 1, characterized in that said engine parameter is a primary or secondary ignition pulse of the engine (15) . 3. A liquefied petroleum gas supply system as defined in claim 1 or 2, characterized in that the electrical signal indicative of air flow-rate in said airstream is a voltage signal proportional to the air flow-rate and generated by an air-flow transducer (16) . 4. A liquefied petroleum gas supply system as defined in claim 3, characterized in that said air flow- rate transducer is a flap (11) , movable in response to the rate of air flow, the movement of said flap operating a transducer element (20) to generate said second electrical signal. WIPO ^NATIO CLAIMS 5. A liquefied petroleum gas supply system as defined in any preceding claim, characterized in that further electrical signals indicative of fuel parameters are supplied to the control unit (17) and the control unit operates the injector means (14) in accordance with all the electrical signals supplied to the control unit. 6. . A liquefied petroleum gas supply system as defined in claim 5, wherein the further electrical signal are generated by thermistors (114, 116) located to measur fuel temperature at the fuel storage container (10) and adjacent the injector means (14). 7. A liquefied petroleum gas supply system as defined in any preceding claim, characterized in that the system includes a fuel cooling arrangement. 8. A liquefied petroleum gas supply system as defined in claim 7, characterized in that the fuel coolin arrangement includes a subsidiary fuel line (100) branchi from a main fuel line (13) , the fuel flow in said subsidiary fuel line being controlled by a thermal lock valve (102) , the fuel line terminating in a nipple (104) which allows liquid fuel to flow into a jacket (106) surrounding a portion of the main fuel line in proximity to the injector means (14) , causing the liquid to vapouriz in said jacket, absorbing heat from the main fuel line, t control unit (17) controlling the thermal lock valve in accordance with signals provided from the thermistor 116 located in proximity to the injector means. 9. A liquefied petroleum gas supply system as defined in claim 8, wherein the low pressure gas is fed t the inlet airstream of the engine (15) . 10. A liquefied petroleum gas supply system as defined in claim 8, wherein the low pressure gas is liquefied by a pump (112) and returned to the main fuel line (13) . O . WIP • - 15 - 11. A liquefied petroleum gas supply system as defined in any preceding claim, characterized in that a main lock valve (12) is provided in the main line (13) . 12. A liquefied petroleum gas supply system as defined in claim 11, characterized in that the control unit (17) is adapted to close the main lock valve (12) and the thermal lock valve (102) , if the ignition sequence fails to start the engine (15) . 13. A liquefied petroleum gas supply system as defined in any preceding claim, characterized in that said injector means is at least one electrically operated fuel injector.

Inventors: COSTA G, YIANNI A
Applicants: COSTA G, YIANNI A
Application year: 1980
Main classification: F02D19
IPC codes: F02D19, F02D41, F02M21