AU682115B2

AU682115B2 - Controller for a LPG system for automobiles

Info

Publication number: AU682115B2
Application number: AU25021/95A
Authority: AU
Inventors: Ilario Dimasi
Original assignee: ISSAC HOLDING Pty Ltd
Current assignee: ISSAC HOLDING Pty Ltd
Priority date: 1994-08-02
Filing date: 1995-07-14
Publication date: 1997-09-18
Anticipated expiration: 2015-07-14
Also published as: AU2502195A

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT (Original) APPLICATION NO:

LODGED:

COMPLETE SPECIFICATION LODGED:

ACCEPTED:

PUBLISHED:

RELATED ART: NAME OF APPLICANT: IS SAC HOLDINGS PTY LTD r r ACTUAL INVENTOR: ADDRESS FOR SERVICE: INVENTION TITLE: ILARIO DIMASI KELVIN LORD AND COMPANY, Patent Trade Mark Attorneys, of 4 Douro Place, West Perth, Western Australia, 6005, AUSTRALIA.

"CONTROLLER FOR A LPG SYSTEM FOR AUTOMOBILES" DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO'S: Australian Provisional Patent Application No. PM 7189 Filed August 2 1994 The following Statement is a full description of this invention including the best method of performing it known to me/us:

-I-

The present invention relates to a controller for a duel fuel engine. More particularly the present invention relates to an electronic controller for a duel fuel engine.

In this specification, the terms "gas" and "LPG" are used interchangably.

Duel Fuel engines are frequently used on automobiles, predominantly on taxis and the like.

However there are known problems with current duel fuel controllers, and some of these problems are set out below.

The main problem with present controllers is that of backfiring, It is common for a car's engine to backfire when running on liquid petroleum gas (LPG), Backfiring can be caused by a number of situations. For example starting the car's engine whilst the setting is switched to gas will frequently cause the engine to backfire. Further, operating the engine on LPG whilst the level of fuel in the LPG tank is too low may cause the car to backfire.

Still further, changing the mode of operation from petrol to gas whilst the throttle, or accelerator pedal is depressed will typically cause the engine to backfire.

Many of the present controllers for duel fuel engines have some form of processing to 15 control the fuel mixture received by the engine when the engine is operating on LPG.

However there are also problems associated with such processing at present. For example many such adaptive processes have a learning span of eight to ten minutes. That is, the adaptive processor will take into account the operation of the engine in the previous eight to ten minutes, but does not remember anything before that time. This can cause problems particularly if the engine is left idling for eight to ten minutes since performance is seriously degraded when the ;rigine is then asked to perform.

Further, many of the present controllers have preset values for such quantities as the fuel mixture when operating on LPG, effectively denying the ability for the installer to tune the engine when running on LPG. An installer can not adjust whether the engine runs on a lean or a rich mixture of LPG since this is preset internally on the controller and is not adjustable.

The present invention seeks to provide a controller for a duel fuel engine which addresses at least some of the above problems.

In accordance with one aspect of the present invention there is provided a controller for a duel fuel engine, including; 1. a microprocessor; 2. adjustment means input to the microprocessor to influence the microprocessor when determining one or more of the following: a) a throttle position beyond which changeover from petrol to LPG should not occur; b) a fuel mixture when using LPG as a fuel; c) a minimum delay after starting the engine before switching from petrol to

LPG;

d) a length of time to operate both petrol and LPG as fuel simultaneously when changing from petrol to LPG; or 3. an interface means, controlled by the microprocessor; S" 4. a first cut off means which, when activated, prevents petrol being used as fuel, a second cut off means which when activated prevents LPG being used as a fuel; a means to control the rate of flow of LPG into the engine when LPG in used as a fuel, wherein the microprocessor controls, through the interface means, the first cut-off means, the second cut-off means, and the flow control means.

The controller of the present invention also preferably includes a petrol fuel pump and a set value for a level of fuel in the LPG gas tank below which the engine should switch to •petrol.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a functional block diagram of the circuit of a controller for a duel fuel engine in accordance with the present invention, and Figures 2Ato 2H show a flow chart for a program to be used in the controller shown in Figure 1.

Figures 3A to 3E show a second flow chart for a program to be used in the controller shown in Figure 1.

Shown in Figure 1 is a controller 10 for a duel fuel engine. The controller 10 comprises a microprocessor 12, a power supply 14, an indicator panel 16, buffering circuitry 18, and 22, and an adjustable throttle dcvice 24, an adjustable fuel device 26, a first adjustable changeover time device 28, second adjustable conversion time device 30 and a set value.

Typically a printed circuit board would be used to house the components of the controller enclosed by a box 34.

The controller 10 further comprises a stepper motor control valve 36, a gas solenoid 38 and a petrol relay 40. Also shown in Figure 1 are a fuel pump 42, a throttle position sensor 44, an oxygen sensor 46, an engine coil negative terminal 48 and a gas tank level indicator In Figure 1 a thin line is used to indicate both a physical connection and a flow of 15 information whilst thick set lines around the microprocessor 12 show the direction of communication between the microprocessor 12 and the indicator panel 16 and the buffering circuitry 18, 20 and 22.

The fuel pump 42, which is used to pump petrol into the engine, the engine's coil negative terminal 48 and the gas tank level indicator 50 are all standard parts of a duel fuel engine.

°°eool The throttle position serisor 44, the oxygen sensor 46, the engine's coil negative terminal 48 and the gas tank level indicator 50) provide information to the controller 10 about the current operating condition of the engine. The throttle position sensor 44 provides information as to the position of the throttle, for example whether or not and the extent to which the accelerator pedal is depressed. The oxygen sensor 46 provides information on the fuel-air mixture which is being fed into a converter. The engine's coil negative terminal 48 provides information as to whether or not the engine is currently operating.

The gas tank level indicator 50 provides information on the amount of LPG fuel remaining in the gas tank. The buffering circuitry 20 is used to convert information received from i the throttle position sensor 44, the oxygen sensor 46, the engine's coil negative terminal 48 and the gas tank level indicator 50 into a format readable by the microprocessor 12.

Further, the buffering circuitry 20 provides protection to the microprocessor 12 against potentially high voltages being input to the buffering circuitry 20. Information received from the buffering circuitry 20 by the microprocessor 12 influences decisions the microprocessor 12 may make.

Further information is fed to the microprocessor 12 from the buffering circuitry 18. The buffering circuitry 18 converts information received from the adjustment devices 24, 26, 28 and 30 into a format readable by the microprocessor 12. The adjustment devices 24, 26, 28 and 30 provide the ability to control the parameters within which the microprocessor 12 makes decisions. The adjustment device 24 is used to set the minimum :i throttle position. That is the adjustment device 24 tells the microprocessor 12 the throttle position at which the accelerator pedal has not been depressed.

The adjustment device 26 is used to set the setting mixture for fuel when the engine is 15 running on LPG. Altering the adjustment device 26 alters whether or not the engine runs on a lean or a rich fuel mixture.

The adjustment device 28 is used to determine the minimum time delay between the "engine starting and changeover from petrol to LPG.

Adjustment device 30 is used to control the time period which both LPG and petrol are used simultaneously when converting from petrol to LPG as fuel.

A set value is used to indicate the predetermined level of fuel in the gas tank at which use ofLPG as a fuel should be ceased and the engine should switch to petrol.

The indicator panel 16 is used to provide the driver of the vehicle with information as to the current status of the vehicle. Such information includes whether or not the vehicle is running on LPG or petrol, or both, the level of fuel in the gas tank as well as sounding alarms in prescribed circumstances.

The high powered buffering and protection circuitry 22 is controlled by the microprocessor 12 and is used to convert signals received from the microprocessor 12 into a form which can be used to directly control the stepper motor control valve 36, the fuel pump 42, the gas solenoid 38 and the petrol relay The gas solenoid 38 is used to control whether or not LPG is used as a fuel in the engine.

The gas solenoid 38 is typically placed in the supply line from the gas tank and when so controlled prevents gas from flowing therethrough.

The petrol relay 40 operates in a similar manner to the gas solenoid 38 to control whether petrol is used as a fuel in the engine.

The stepper motor control valve 36 is used to control the amount of LPG which flows into the engine and is thus used by the microprocessor 12 to control the mixture of fuel used in the engine. The fuel pump 42 is a standard fuel pump used in petrol engines and control of the iuel pump 42 by the microprocessor 12 is desirable since it is highly desirable that when the engine is operating on LPG, the fuel pump 42 is activated periodically for a short period of time.

Shown in figures 2A to 2H of the drawings is a flow chart for a computer program to operate in the controller 10. It should be noted that when viewing Figures 2A to 2H that the right-hand side of Figure 2A leads to the left-hand side of Figure 2B and the righthand side of Figure 2B leads to the left-hand side of Figure 2C and so on. The operation of the computer program as outlined in the flow chart in Figures 2Ato 2H will now be described.

Initially when the engine is started the throttle position sensor 44 is read. If the throttle position 44 is not in the home position, as determined by the adjustment device 24 an :I audio alarm is sounded. The car will not be started until the throttle position sensor 44 indicates that the throttle is in an idle position. Therefore the car can not be started with the accelerator pedal depre,;sed, reducing the risk of a backfire.

The engine is then started and runs on petrol. This is irrespective of whether or not the operator has selected the vehicle run on gas or petrol since starting a duel fuel engine on LPG can cause the engine to backfire. If the engine is started with the operator selecting operation of gas then after a period of time determined by the adjustment means 28 the vehicle begins to operate on both petrol and LPG. After a period of time determined by the adjustment means 30 the vehicle then operates only on LPG. Control of whether the vehicle runs on LPG or petrol is determined by activating or deactivating the gas solenoid 38 and the petrol relay 40. The time delay when converting from petrol to gas during which the engine operates on both petrol and LPG is desirable to prevent misfiring of the engine during switch over. An initial delay between starting the engine and changing over to duel fuel and then LPG only operation is desirable to allow the engine to warm slightly before the introduction of LPG into the engine.

The controller 10 will not allow the vehicle to be operated on LPG if there is insufficient gas in the gas tank. Therefore if the engine is started with the switch set to gas the car will be started on petrol as previously described, however the controller will not switch over •to the use of LPG if there is insufficient fuel in the gas tank compared with the predetermined level set by the set value.

When the engine is running on LPG and the level of gas in the gas tank falls to a level 15 which is approaching the level determined from the set value, an audible alarm will sound and a light will flash to indicate to the driver that the level of gas in the gas tank is getting low. As the level of gas in the gas tank reduces further the audible alarm sounds more S"frequently. If more gas is not fed into the gas tank then when the level of gas in the gas tank falls to that determined by the set value, the engine will automatically switch back to the use of petrol irrespective of the position of the operator selection switch. Thus the engine will not continue to run on LPG if there is insufficient gas in the gas tank and a risk of backfire or misfiring is present. The amount of gas in the gas tank which constitutes a dangerously low level is preset.

When the engine is running on gas and the operator switches the selection switch from LPG to petrol the engine automatically switches back to petrol. If the operator were to then switch the car over to LPG the controller would again institute a duel fuel time during which both petrol and LPG would be operated before switching over to LPG only.

Tlis is to ensure a smooth change over from petrol to LPG without misfiring. A duel fuel 8 time is not necessary when switching from LPG to petrol as there is almost no chance of a misfire in that operation.

When the engine is rurming on LPG only the controller 12 will activate the fuel pump 42 for a two minute period once every 15 minute?. As previously mentioned this is to prevent unwanted blockages and staling of the petrol occurring in the injectors of the engine.

When the engine is running on petrol only, as indicated by the operator switch indicating petrol use, the controller does not actively control the running of the engine. Instead it simply monitors the status of the operator switch and waits for the operator switch to indicate that the operator would like the vehicle to operate on LPG.

Information on the amount of gas in the gas tank is provided to the microprocessor 12 by the gas tank level indicator 50. Information as to whether or not the engine is currently running is provided to the microprocessor 12 by the engine's coil negative terminal 48.

SWhen the engine is operating on LPG the microprocessor 12 controls the mixture of the fuel into the engine. This is achieved by the microprocessor 12 reading the throttle 15 position sensor 44 and comparing the value read with the previous value read from the throttle position sensor 44. If there has been no change in the position of the throttle then the microprocessor 12 determines the appropriate mixture according to the mi::ilre .setting determined by the adjustment means 24 and information received from the oxygen sensor 46. The microprocessor 12 then controls, via the buffering circuitry 22, the stepper V motor control valve 36 to appropriately control and adjust the mixture of fuel in the engine.

If, however, reading the throttle position sensor 44 indicates that the position of the ithrottle has moved then the new position of the throttle is used to determine the reference point. If the throttle has moved to a smaller value, that is if the accelerator pedal has been eased off, then the microprocessor 12 will continue to process the mixture according to the adjustment device 24 and informati n received from the oxygen sensor 46. However if the change in the throttle indicates that the throttle has increased, that is that the accelerator has been depressed, then the microprocessor 12 suspends processing an appropriate mixture and operates the stepper motor control valve 36 to give a full rich mixture irrespective of the position of the adjustment means 24.

By the above process power is provided to the engine when needed, i.e. when the accelerator pedal is depressed. When the accelerator pedal is held at a constant level or decreased the microprocessor 12 will adjust the mix of the fuel to give an efficient operation.

The controller of the present invention provides a controller for a duel fuel engine which includes safety features such as automatically returning to petrol operation if the engine stalls or is turned off. The controller 10 will not allow the vehicle's engine to start on gas under any condition. Further an adjustable automatic change over delay from petrol to gas once the vehicle has been started can be achieved by use of adjustment means 28. An adjustable automatic duel fuel time on which the vehicle operates on both petrol and gas S. during the change over from petrol to gas for smooth change overs is provided and can be adjusted by means of adjustment means 30. The microprocessor 12 will further turn on the petrol fuel pump for two minutes in every 15 minutes whilst running on LPG.

Further, the adjustment means 26 allows for the installer or an operator to adjust the fuel mixer setting for running the engine on a lear, or a rich mixture. The controller 10 of the present invention also automatically switches back to petrol if the level of LPG in the gas tank is too low, with an audible alarm telling the operator before that the tank level is 20 approaching this point. The controller 10 will not change to gas if the operator has the accelerator pedal depressed at time of changeover. An audible alarm will sound until the accelerator pedal is released. Finally the present invention provides processing of the current status of the vehicle to provide a response which gives a rich mixture for power when needed and provides control over the mixture when full power is not required.

The controller of the present invention further provides a controller 10 for a duel fuel engine wherein allowance is made for failure of the oxygen sensor 46. The oxygen sensor 46 typically will send a voltage in a range from 0.00 to 0.95 volts. When the microprocessor receives no voltage, or a voltage substantially outside the typical range to indicate failure, the microprocessor will run on preset memory values rather than reading the information from the oxygen sensor 46. Whilst the engine is running on LPG the microprocessor will cut off oxygen sensor voltage to a vehicle's electric control unit (ECU). The controller 10 when having detected failure of the oxygen sensor 46 will set optimum mixture settings for a duel fuel engine according to preset memory values. This may include altering the stepper motor control valve settings to compensate for oxygen sensor failure or engine wear and tear. Hence, the microprocessor will run under open loop con&dions when it senses an oxygen sensor 46 failure. In addition, an audible alarm will sound and a flashing light will tell the driver that the oxygen sensor 46 has failed.

The controller also has an implemented diagnostic test which can be accessed via pushing a button on the operator panel 16 which is positioned in the vehicle. The pushed button will access a test which compares the values of the adjustable devices 24, 26, 28, 30, a set ".to value, oxygen sensor 46, throttle position sensor 44, engine's coil negative terminal and 99 gas tank level indicator 50 with preset memory values. The microprocessor 12 then 15 adjusts the amount of LPG to flow into the engine, by way of the stepper motor control valve 36, which controls whether the gas/air mixture is in the preset memory value range.

When this test is accessed, the vehicle's engine should be running at approximately 3000 to revolutions/minute. This diagnostic test has the advantage of alleviating the need for a gas analyser.

Modifications and variations such as would be apparent to a skilled addressee are deemed within the scope of the present invention, I i rslr

Claims

2. an adjustment means input to the microprocessor to influence the microprocessor when determining one or more of the following: a) a throttle position beyond which changeover from petrol to LPG should not occur; b) a fuel mixture when using LPG as a fuel; c) a minimum delay after starting the engine before switching from petrol to LPG; or d) a length of time to operate both petrol and LPG as fuel simultaneously oeooo when changing from petrol to LPG; an interface means, controlled by the microprocessor; a first cut off means which, when activated, prevents petrol being used as fuel; a second cut off means which when activated prevents LPG being used as a fuel; and
6. a means to control the rate of flow of LPG into the engirne when LPG is -•used as a fuel; wherein the microprocessor controls, through the interface means, the first cut-offmeans, the second cut-offmeans, and the flow control means. 2. A controller for a dual fuel engine according to claim 1, wherein the microprocessor has a set value for a level of fuel in the LPG gas tank below which the engine should switch to petrol. 3. A controller for a dual fuel engine according to claim I or 2, wherein the microprocessor controls through the interface means a petrol fuel pump. 4. A controller for a dual fuel engine according to claim 1 or 2 or 3, wherein the adjustment means input includes one or more of an adjustable throttle device, an mt,.'mmmmt* *a, 12 adjustable fuel device, a first adjustable changeover time det and a second adjustable conversion time device. A controller for a dual fuel engine according to any one of claims 1 to 4, wherein the microprocessor is arranged to detect a lean mixture of LPG for a period of time and means is provided for switching the engine to use petrol if the lean mixture of LPG is maintained for a predetermined length of time, 6. A controller for a dual fuel engine according to any one of the preceding claims, wherein the first cut-off means is a petrol relay.
7. A controller for a dual fuel engine according to any one of the preceding claims, wherein the second cut-offmeans is a gas solenoid.
8. A controller for a dual fuel engine according to any one of the preceding claims, :wherein the flow control means is a stepper motor control valve.
9. A controller for a dual fuel engine according to any one of the preceding claims, wherein the microprotessor includes the feature of detecting failure of an oxygen sensor, 10, A controller fot a dual fuel engine according to claim 9, wherein the controller, whilst the engine is running on LPG, will cut off oxygen sensor voltage to an ECU of a vehicle so that the ECU does not write into its memory the conditions of that gas. 11, A controller for a dual fuel engine according to claim 9 or 10, wherein the controller will set an optimum mixture setting for a dual fuel engine under open loop conditions.
12. A controller for a dual fuel engine according to any one of claims 8 to 11, wherein the controller undergoes an implemented sclf learning process to alter the stepper motor control valve settings to compensate for oxygen sensor failure or engine wear and tear,
13. A controller for a dual fuel engine according to any one of the preceding claims, wherein the controller has an implemented diagnostics test whereby the engine's performance can be analysed and corrected without a need of a gas analyser.
14. A controller for a dual fuel engine according to any one of the preceding claims, where an implemented circuitry reads all tachometer voltages and requires no booster or signal amplifier. A controller for a dual fuel engine according to any one of the preceding claims, in which the adjustment means is arranged to influence the microprocessor when determining any two or more or any three or more of the parameters to
16. A controller for a dual fuel engine substantially as hereinbefore described with reference to any one of the accompanying drawings. DATED THIS 4TH DAY OF July 1997 ISSAC HOLDINGS PTY LTD By their Patent Attorneys KELVIN LORD AND COMPANY 15 PERTH, WESTERN AUSTRALIA •o0 f e *o o 14 ABSTRACT A controller (10) for a duel fuel engine including a microprocessor adjustment means input (24, 26, 28 and 30), nd interface means (16, 18, 20 and 22), a first cut off means a second cut off means (38) which controls the rate of flow of LPG into the engine when LPG is used as a fuel. *tooS .06 6*