JP3067293B2 - Air-fuel ratio control device for LPG engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquefied petroleum gas (LP)
The present invention relates to an LPG engine using G) as fuel, and more particularly, to an air-fuel ratio control device for controlling the air-fuel ratio.

[0002]

2. Description of the Related Art Conventionally, as this kind of technology, for example, an "air-fuel ratio control device for an LPG engine" disclosed in Japanese Patent Application Laid-Open No. 1-200053 is already known. In this technique, a main fuel is supplied to a venturi formed in an intake passage of an LPG engine via a normal fuel passage (main fuel passage). Then, the main fuel and the intake air are mixed in the venturi, and the air-fuel mixture is supplied to each cylinder of the engine body. In the middle of the main fuel passage, there is provided a variable opening control valve using a stepping motor as a drive source, and the supply amount of the main fuel is controlled by opening and closing the control valve. An injector is provided in an intake passage downstream of the venturi, and a part of idle slow fuel is injected and supplied as auxiliary fuel from the injector to the intake passage. The fuel injection amount of the injector is controlled by controlling the injection time.

In the technology disclosed in this publication, LPG
When the engine is not in a high load state, that is, when the engine is at a medium to light load, the control valve of the main fuel passage is opened and closed by a step motor so that the air-fuel ratio becomes lean, and the main fuel is supplied to the venturi. At the same time, by increasing or decreasing the injection amount of the auxiliary fuel from the injector, the air-fuel ratio adjusted to the lean side by the supply of the main fuel is set to the stoichiometric air-fuel ratio.
The air-fuel ratio feedback control was executed.
At this time, in order to bring the air-fuel ratio closer to the stoichiometric air-fuel ratio, an air-fuel ratio correction coefficient (FAF) is calculated and determined based on the oxygen concentration in the exhaust gas detected by an oxygen sensor provided in the exhaust passage.
The air-fuel ratio feedback control is executed based on the air-fuel ratio correction coefficient.

On the other hand, when the LPG engine is under a high load condition, that is, when the throttle valve is fully opened, the control valve in the main fuel passage is opened / closed by a step motor to increase / decrease the amount of main fuel supplied to the venturi. In addition, the air-fuel ratio feedback control is performed so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. At this time, in order to bring the air-fuel ratio closer to the stoichiometric air-fuel ratio, the air-fuel ratio correction coefficient is also calculated and determined based on the oxygen concentration detected by the oxygen sensor, and the air-fuel ratio feedback control is executed based on the air-fuel ratio correction coefficient. I was

[0005]

Therefore, in the above-mentioned prior art, the mode of the air-fuel ratio feedback control is switched between when the LPG engine is lightly loaded and when it is heavily loaded. That is, the control mode is switched between the control mode of the auxiliary fuel supply by the injector and the control mode of the main fuel supply by the step motor. Therefore, when the air-fuel ratio correction coefficient having the same value is continuously used in the air-fuel ratio feedback control before and after the switching between the two control modes, a problem may occur. That is, since the correction amount per unit of the air-fuel ratio correction coefficient is different between the two control modes, immediately after switching of the control mode, the air-fuel ratio obtained by the feedback control due to the shift of the correction amount may be significantly deviated. was there. In addition, as a result, there is a possibility that drivability and exhaust emission may be deteriorated.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to prevent a large deviation in the air-fuel ratio when the control mode is switched between the main fuel supply and the auxiliary fuel supply. It is another object of the present invention to provide an air-fuel ratio control device for an LPG engine that can prevent deterioration in drivability and exhaust emission.

[0007]

In order to achieve the above object, according to the present invention, as shown in FIG. 1, a venturi M3 formed in an intake passage M2 of an engine M1 using liquefied petroleum gas as a fuel is provided. Main fuel mixing means M4 for mixing the main fuel with the intake air via the main fuel mixing means and supplying the air-fuel mixture to the engine M1, and an intake passage M2 provided at a position different from the main fuel mixing means M4. And an auxiliary fuel injection means M5 for injecting auxiliary fuel into the exhaust passage M6 of the engine M1.
Air-fuel ratio detecting means M7 for detecting the air-fuel ratio of the fuel supply, and the amount of mixture supplied by the main fuel mixing means M4 and the auxiliary fuel injection means M5
A correction coefficient calculating means M8 for calculating an air-fuel ratio correction coefficient based on the air-fuel ratio detected by the air-fuel ratio detecting means M7, and an operation load state of the engine M1 for correcting the auxiliary fuel injection amount from the engine M1 respectively. Load state detecting means M9
When the detection result of the load state detecting means M9 is a high load state, the amount of air-fuel mixture supplied by the main fuel mixing means M4 is increased or decreased based on the air-fuel ratio correction coefficient calculated by the correction coefficient calculating means M8. When the detection result of the high-load control means M10 for performing the air-fuel ratio feedback control by means of the load control means M9 and the load state detection means M9 indicates a medium-to-light load state, the correction coefficient calculation means M8 In the air-fuel ratio control device of the LPG engine including the medium-light load control means M11 for performing the air-fuel ratio feedback control by increasing or decreasing the air-fuel ratio based on the air-fuel ratio correction coefficient calculated by When the control mode is switched between the feedback control and the air-fuel ratio feedback control by the medium / light load control unit M11, the control mode corresponding to the switch mode is changed The air-fuel ratio correction coefficient which is use is provided a correction coefficient initialization means M12 for initializing.

[0008]

According to the above construction, as shown in FIG. 1, the main fuel mixing means M4 mixes the main fuel of liquefied petroleum gas (LPG) with the intake air through the venturi M3 of the intake passage M2. The mixture is supplied to the engine M1. The auxiliary fuel injection means M5 injects LPG auxiliary fuel into the intake passage M2 at a position different from that of the main fuel mixing means M4. Then, the engine M1 takes in the air-fuel mixture or the auxiliary fuel, explodes and burns to obtain a driving force, and then discharges the exhaust gas through the exhaust passage M6.

During the operation of the engine M1, the air-fuel ratio detecting means M7 detects the air-fuel ratio of the engine M1 from the oxygen concentration in the exhaust gas. The correction coefficient calculating means M8
Is to correct the air-fuel ratio based on the air-fuel ratio detected by the air-fuel ratio detection means M7 in order to correct the air-fuel ratio supplied by the main fuel mixing means M4 and the auxiliary fuel injection amount from the auxiliary fuel injection means M5, respectively. Calculate the coefficient. Further, the load state detecting means M9 detects the operating load state of the engine M1.

Here, when the detection result of the load state detecting means M9 indicates a high load state, the high load control means M1
In the case of 0, the air-fuel ratio feedback control is performed by increasing or decreasing the air-fuel mixture supply amount by the main fuel mixing means M4 based on the air-fuel ratio correction coefficient calculated by the correction coefficient calculation means M8. on the other hand,
When the detection result of the load state detecting means M9 is a medium to light load state, the medium / light load control means M11 calculates the auxiliary fuel injection amount from the auxiliary fuel injection means M5 by the correction coefficient calculating means M8. The air-fuel ratio feedback control is performed by increasing or decreasing the value based on the fuel ratio correction coefficient.

Then, the air-fuel ratio feedback control by the high load control means M10 is changed to the medium light load control means M11.
When the control mode is switched to the air-fuel ratio feedback control by the control mode, or when the control mode is switched from the air-fuel ratio feedback control by the medium-light load control means M11 to the air-fuel ratio feedback control by the high load control means M10, the control mode after the switching is performed. Are initialized by the correction coefficient initialization means M12.

Therefore, when the control mode is switched, the air-fuel ratio correction coefficient is initialized once regardless of whether the load is high or medium to light. Therefore, even if the correction amount per unit related to the air-fuel ratio correction coefficient differs between the control modes, the air-fuel ratio immediately after the control mode switching is properly corrected.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an air-fuel ratio control apparatus for an LPG engine according to the present invention will be described in detail with reference to FIGS.

FIG. 2 is a schematic configuration diagram showing an engine system to which the air-fuel ratio control device of the LPG engine in this embodiment is applied. The LPG engine 1 using liquefied petroleum gas (LPG) as a fuel includes a plurality of cylinders (only one cylinder is shown in FIG. 2). The engine 1 is connected to an air cleaner 3 via an intake passage 2. A venturi 4 is provided in the middle of the intake passage 2. Also, the intake passage 2
Inside, a throttle valve 5 is provided downstream of the venturi 4 to open and close in response to operation of an accelerator pedal (not shown). When the throttle valve 5 is opened and closed, the amount of intake air from the air cleaner 3 to the intake passage 2 is adjusted. Each cylinder of the LPG engine 1 is provided with a spark plug 6. On the other hand, a three-way catalyst 8 is provided in an exhaust passage 7 communicating with the LPG engine 1. Further, a well-known exhaust gas recirculation device 9 is provided between the exhaust passage 7 and the intake passage 2.

An ignition signal distributed by a distributor 10 is applied to an ignition plug 6 provided for each cylinder of the LPG engine 1. The distributor 10 distributes the high voltage output from the igniter 11 to each spark plug 6 in synchronization with the crank angle of the LPG engine 1. The ignition timing of each ignition plug 6 is determined by the high voltage output timing from the igniter 11. The distributor 10 is provided with a rotation speed sensor 31 for detecting the rotation speed (engine speed) NE of the LPG engine 1 from the rotation of the rotor.

The venturi 4 of the intake passage 2 has an LP
One end of a main fuel passage 12 for supplying G as a main fuel is in communication. The other end of the main fuel passage 12 is connected to an LPG regulator 1 for adjusting LPG vaporization.
3 is communicated.

A fuel throttle valve 15 driven by a step motor 14 is provided in the main fuel passage 12.
A main fuel mixing means is constituted by the main fuel passage 12 and the fuel throttle valve 15. The opening of the main fuel passage 12 is adjusted by controlling the drive of the fuel throttle valve 15. The amount of main fuel supplied to LPG engine 1 is adjusted.

On the upstream side of the fuel throttle valve 15, the base end of the main fuel passage 12 is connected to a secondary pressure reducing chamber 13 b of the LPG regulator 13. Also, the main fuel passage 12
In the vicinity of the base end of the LPG regulator 13, there is provided a slow fuel passage 16 that communicates with the primary pressure reducing chamber 13 a of the LPG regulator 13 and supplies the slow fuel for idling. In the middle of the slow fuel passage 16, near the junction with the main fuel passage 12, an idle adjust screw 13 c for slow fuel adjustment is provided.

When the LPG engine 1 is operating,
Outside air is sucked from the air cleaner 3 through the intake passage 2. Also, at the time of inhalation of the outside air, Venturi 4 has LP
The main fuel from the G regulator 13 is led out through the main fuel passage 12, and the main fuel is mixed with the intake air.
The mixture is taken into the LPG engine 1. still,
The intake amount of the main fuel mixture in the LPG engine 1 is determined by the opening of the throttle valve 5.

On the other hand, an injector 17 as auxiliary fuel injection means is provided in the intake passage 2 downstream of the throttle valve 5. The injector 17 is connected to an auxiliary fuel passage 18 communicating with the slow fuel passage 16. Then, the injector 17 injects a part of the idle slow fuel sent from the primary pressure reducing chamber 13a of the LPG regulator 13 via the auxiliary fuel passage 18 into the intake passage 2 as auxiliary fuel. The injected auxiliary fuel and intake air are taken into the LPG engine 1. The LPG regulator 13 is provided with a slow lock valve 20 driven by a solenoid 19 to open and close the slow fuel passage 16. The opening / closing of the slow lock valve 20 is controlled to perform a fuel cut or the like at the time of deceleration.

Therefore, the LPG engine 1 takes in the main fuel mixture or the auxiliary fuel, explodes and burns to obtain a driving force, and then discharges the exhaust gas to the exhaust passage 7. Exhaust gas discharged from the LPG engine 1 to the exhaust passage 7 is purified while passing through the three-way catalyst 8, and is discharged to the outside. At the same time, part of the exhaust gas passing through the exhaust passage 7 is recirculated to the intake system by the exhaust gas recirculation device 9.

In order to detect the operating state of the LPG engine 1 and the like, the intake passage 2 is provided with an intake air temperature sensor 32 for detecting the temperature (intake air temperature) THA of the outside air sucked from the air cleaner 3. A throttle sensor 33 for detecting the opening (throttle opening) VL is provided near the throttle valve 5. Similarly, the intake passage 2 is provided with an intake pressure sensor 34 for detecting the pressure of the intake air (intake pressure). The throttle sensor 33 and the intake pressure sensor 34 constitute load state detecting means for detecting the operation load state of the LPG engine 1.
Further, the LPG engine 1 is provided with a water temperature sensor 35 for detecting the cooling water temperature THW. On the other hand, the exhaust passage 7 is provided with an oxygen sensor 36 as air-fuel ratio detecting means for detecting the air-fuel ratio of the LPG engine 1 from the oxygen concentration in the exhaust gas discharged from the exhaust passage 7. Similarly, the exhaust passage 7 is provided with an exhaust gas temperature sensor 37 for detecting the temperature of the exhaust gas (exhaust gas temperature).

The step motor 14 of the fuel throttle valve 15, the solenoid 19 of the slow lock valve 20,
The injector 17 and the igniter 11 are electronic control units (hereinafter simply referred to as “E”) that constitute a correction coefficient calculation unit, a high load control unit, a medium / light load control unit, and a correction coefficient initialization unit.
CU ”) 38. The ECU 38 includes a rotation speed sensor 31 and an intake air temperature sensor 3.
2. A throttle sensor 33, an intake pressure sensor 34, a water temperature sensor 35, an oxygen sensor 36, an exhaust temperature sensor 37, and the like are connected to each other. Then, based on the detection signals output from each of the sensors 31 to 37, the ECU 38 controls the step motor 14, the solenoid 19, the injector 17
And the igniter 11 and the like are suitably controlled.

Next, the configuration of the ECU 38 will be described with reference to the block diagram of FIG. The ECU 38 includes a central processing unit (CPU) 41, a read-only memory (ROM) 42 in which a predetermined control program and the like are stored in advance, and a random access memory (R) that temporarily stores calculation results of the CPU 41 and the like.
AM) 43, a backup RAM 44 for storing data stored in advance, and the like, and a logical operation circuit in which these components are connected to an external input circuit 45, an external output circuit 46, and the like via a bus 47.

The external input circuit 45 includes a rotation speed sensor 31, an intake air temperature sensor 32, a throttle sensor 33,
An intake pressure sensor 34, a water temperature sensor 35, an oxygen sensor 36, an exhaust temperature sensor 37, and the like are connected to each other. Then, the CPU 41 transmits each sensor 3 via the external input circuit 45.
The detection signals output from 1 to 37 are read as input values. The CPU 41 suitably controls the igniter 11, the step motor 14, the injector 17, the solenoid 19, and the like connected to the external output circuit 46 based on these input values.

Next, the processing operation of the air-fuel ratio control of the LPG engine 1 executed by the aforementioned ECU 38 will be described with reference to the flowcharts shown in FIGS.
FIG. 4 is a flowchart showing a "main routine" process related to the opening / closing control of the fuel throttle valve 15 and the opening / closing control of the injector 17 among the processes executed by the ECU 38. Be executed.

When the process proceeds to this routine, first, at step 100, a process of "ST calculation routine" for calculating a target number ST of the step motor 14 in the fuel throttle valve 15 is executed.

Next, at step 200, the processing of a "FAF calculation routine" for calculating an air-fuel ratio correction coefficient FAF for air-fuel ratio feedback control is executed.
Subsequently, in step 300, a process of a “learning routine” for further improving the control accuracy to the stoichiometric air-fuel ratio is executed.

Further, in step 400, a process of a "TAU calculation routine" for calculating the injection time TAU of the injector 17 is executed, and thereafter, the process of the "main routine" is temporarily terminated.

Next, the processing of steps 100, 200, 300, and 400 in the aforementioned "main routine" will be described in detail. First, step 100
Of the “ST calculation routine” in step 10
The subroutine is called at 0 and executed, as shown in the flowchart of FIG.

When this processing is started, first, in step 1
At 10, the basic step number S of the step motor 14 in the fuel throttle valve 15 is calculated. The basic step number S is obtained by referring to a three-dimensional map (not shown) stored in the ROM 42 in advance based on the engine speed NE and the intake pressure PM obtained by the detection of the rotation speed sensor 31 and the intake pressure sensor 34. The basic step number S of the three-dimensional map is set in advance so that the main fuel supplied through the main fuel passage 12 is on the lean side.

Next, in step 120, a learning correction value KG for correcting the basic step number S is loaded. This learning correction value KG is obtained in the processing of a “learning routine” described later.

In step 130, an intake air temperature correction coefficient FTHA is calculated. This calculation is based on the intake air temperature sensor 3
2 based on the intake air temperature THA obtained by the detection of
This is performed by referring to a two-dimensional map stored in advance in 42.

Further, at step 140, a water temperature correction coefficient FTHW is calculated. This calculation is based on the water temperature sensor 35
Based on the cooling water temperature THW obtained by detecting the
This is performed by referring to a two-dimensional map stored in advance in 42.

Next, at step 150, a feedback correction coefficient FAFST for performing feedback control of the step motor 14 of the fuel throttle valve 15 is loaded. This feedback correction coefficient FAFST is obtained in the processing of the “FAF calculation routine” described later.

In step 160, the learning correction value KG and the intake air temperature correction coefficient FTH are added to the number of basic steps S.
A, the basic step number S is corrected by multiplying each of the water temperature correction coefficient FTHW and the feedback correction coefficient FAFST. Further, the calculation result is set as the target step number ST for the step motor 14, and the subsequent processing is temporarily ended.

Next, the processing of the "FAF calculation routine" will be described. This "FAF calculation routine" is a process that is executed by being called as a subroutine in step 200, and is shown in the flowcharts of FIGS.

First, in step 201, it is determined whether a feedback (F / B) control condition is satisfied. In this embodiment, it is determined based on the detection signals of the water temperature sensor 35 and the rotation speed sensor 31 whether or not the condition that the cooling water temperature THW is sufficiently high and the engine rotation speed NE is not higher than necessary is satisfied. Is done.

Here, if the condition of the feedback control is satisfied, at step 202, the oxygen sensor 3
It is determined whether the air-fuel ratio (A / F) is rich based on the detection signal of No. 6. Then, when the air-fuel ratio is rich, the processing of the following steps 203 to 208 is executed.

That is, in step 203, when the process of the "FAF calculation routine" is executed in the previous control cycle, it is determined whether or not the air-fuel ratio is lean by the air-fuel ratio flag YOX. Here, the air-fuel ratio flag Y
If OX is “0”, the process proceeds to step 204 assuming that the air-fuel ratio has changed from lean to rich based on the determinations in steps 202 and 203.

In step 204, the average air-fuel ratio correction coefficient FA during the air-fuel ratio feedback control is determined.
Calculate FAV. This average air-fuel ratio correction coefficient FAFAV
Is calculated based on the current air-fuel ratio correction coefficient FAF and the old air-fuel ratio correction coefficient FAF obtained when the previous time was changed from rich to lean.
This is performed by calculating an arithmetic mean with zero.

Next, at step 205, the air-fuel ratio correction coefficient FAF is set as the previous old air-fuel ratio correction coefficient FAF0. Subsequently, in step 206, a result obtained by subtracting the predetermined skip amount a from the air-fuel ratio correction coefficient FAF is set as a new air-fuel ratio correction coefficient FAF.

In step 207, since the current air-fuel ratio is rich, the learning timing flag YK
Set G to "1". This learning timing flag Y
KG is used to determine whether or not it is time to learn the learning correction value KG, which will be described later.

Further, at step 208, since the air-fuel ratio is rich, the air-fuel ratio flag YOX is set to "1", and thereafter, the routine proceeds to step 212. On the other hand, when the air-fuel ratio flag YOX is “1” in step 203, the processing of steps 209 to 211 is executed. Here, when the process proceeds to step 209 according to the determination in steps 202 and 203, it indicates that the air-fuel ratio is maintaining a rich state.

That is, in step 209, it is determined whether or not the timer counter CNT1 exceeds a constant c.
The timer counter CNT1 is a value that has a shorter cycle than the processing of the “FAF calculation routine” and is added in the processing of a “compare interrupt routine” described later. here,
If the timer counter CNT1 exceeds the constant c, in step 210, the result obtained by subtracting the constant b from the air-fuel ratio correction coefficient FAF is set as a new air-fuel ratio correction coefficient FAF.

Then, in step 211, after clearing the timer counter CNT1 to "0", the process proceeds to step 212. If it is determined in step 209 that the timer counter CNT1 is equal to or smaller than the constant c, the process directly proceeds to step 212. That is, step 209
In the processing of Step 211, the value of the air-fuel ratio correction coefficient FAF is subtracted by a constant b every predetermined time.

At step 212 after the transition from steps 208, 209 and 211, it is determined whether or not the injector feedback determination flag YFBINJ is "1". This flag YFBINJ indicates that the injector 1
7 indicates whether or not the feedback control should be executed, and is determined according to the flowchart of the “YFBINJ calculation routine” shown in FIG.

Here, the flowchart of the "YFBINJ calculation routine" will be described first. When the processing of this routine is started, first, in step 251, a predetermined constant j is subtracted from a predetermined pressure PMVL indicating the intake pressure when the opening of the throttle valve 5 is large, and the result of the subtraction is referred to as a high load determination pressure PMG. Set as

Next, at step 252, it is determined whether or not the throttle opening VL detected by the throttle sensor 33 is larger than a predetermined value (50 ° in this embodiment). Here, if the throttle opening VL is not larger than the predetermined value, the process directly proceeds to step 254.

If it is determined in step 252 that the throttle opening VL is larger than the predetermined value, the routine proceeds to step 25.
3, the intake pressure P detected by the intake pressure sensor 34
M is set as the next predetermined pressure PMVL, and step 2
Move to 54.

Then, step 252 or step 25
In step 254 after shifting from 3, it is determined whether or not the intake pressure PM detected by the intake pressure sensor 34 is smaller than the previously calculated high load determination pressure PMG. That is,
It is determined whether the load is not high. If the intake pressure PM is smaller than the high load determination pressure PMG, the process proceeds to step 255 on the assumption that the load is not the high load state but the medium light load state. Then, in step 255,
The injector feedback determination flag YFBINJ is set to “1”, and the subsequent processing is temporarily terminated.

On the other hand, if the intake pressure PM is not smaller than the high load determination pressure PMG in step 254, it is determined that the load is high, and in step 257, the injector feedback determination flag YFBI is determined.
NJ is reset to "0", and the subsequent processing is temporarily ended.

Returning to the processing of the "FAF calculation routine" in FIG. 6 again, if the injector feedback determination flag YFBINJ is "1" in step 212,
Assuming that the load is in the middle to light state, the process proceeds to step 213 in order to execute the feedback control of the injector 17. In step 213, the feedback correction coefficient FA for the step motor 14 of the fuel throttle valve 15
Set the value of FST to "1.0".

In step 214, the air-fuel ratio correction coefficient FAF calculated in step 206 or step 210 is set as a feedback correction coefficient FAFINJ for the injector 17.

In step 215, the previous injector feedback determination flag YFBINJ0
Is set to “1”, and the subsequent processing is temporarily ended.
On the other hand, if the injector feedback determination flag YFBINJ is not “1” in step 212, that is, if the load is high, the process proceeds to step 216.

In step 216, it is determined whether or not the previous injector feedback determination flag YFBINJ0 is "1". Here, if the determination flag YFBINJ0 is not “1”, that is, if the load is high in the previous control cycle, the process proceeds to step 21.
Move to 8. If the determination flag YFBINJ0 is "1" in step 216, that is, if the vehicle is in a medium-to-light load state, step 217 is executed in step 216.
06 or the air-fuel ratio correction coefficient FAF calculated in step 210 is initialized to “1.0”, and the process proceeds to step 218.

Then, step 216 or step 21
7, the process proceeds to step 218 where the air-fuel ratio correction coefficient FAF is set to the value of the step motor 14 of the fuel throttle valve 15.
Is set as the feedback correction coefficient FAFST.

In step 219, the feedback correction coefficient FAFINJ for the injector 17 is set to "1.0". Further, the previous injector feedback determination flag YFBINJ0 is reset to “0”, and the subsequent processing is temporarily ended.

The above-mentioned steps 203 to 2
The process at 11 is a process when the air-fuel ratio is rich, and is a process for reducing the air-fuel ratio correction coefficient FAF. In contrast to this processing, the processing in steps 221 to 229 shown in the flowchart of FIG. 7 is processing when the air-fuel ratio is lean, and the air-fuel ratio correction coefficient FA
This is a process for increasing F.

That is, if the air-fuel ratio is lean in step 202, the process proceeds to step 221. In step 221, the air-fuel ratio flag YOX is set to "1".
Is determined. Air-fuel ratio flag YOX is "1"
In the case of, the process proceeds to step 222 assuming that the air-fuel ratio has switched from rich to lean,
In the same manner as in the processing in step 204 described above, the average air-fuel ratio correction coefficient F during the air-fuel ratio feedback control
Calculate AFAV.

Subsequently, in step 223, the value of the air-fuel ratio correction coefficient FAF is set as the old air-fuel ratio correction coefficient FAF0. In step 224, the result of adding the skip amount a to the air-fuel ratio correction coefficient FAF is set as a new air-fuel ratio correction coefficient FAF.

Further, in step 225, the learning timing flag YKG is set to "1". And
In step 226, it is determined that the air-fuel ratio is lean, and the air-fuel ratio flag YOX is reset to “0”.
Is performed.

If the air-fuel ratio flag YOX is "0" at step 221, the processing at steps 227 to 229 is executed. Here, step 2
When the process proceeds from step 21 to step 227, it indicates that the air-fuel ratio is maintaining a lean state.

At step 227, it is determined whether or not the above-mentioned timer counter CNT1 exceeds a constant c.
Here, when the timer counter CNT1 exceeds the constant c, in step 228, the air-fuel ratio correction coefficient FAF
The result of adding the constant b to the air-fuel ratio correction coefficient FAF
Set as

Then, in step 229, after clearing the timer counter CNT1 to "0", the flow shifts to step 212 to execute the processing of steps 212 to 220.

If it is determined in step 227 that the timer counter CNT1 is equal to or smaller than the constant c, the flow directly proceeds to step 212. That is, the processing in steps 227 to 229 is the opposite of the processing in steps 209 to 211 described above, and is a processing for increasing the value of the air-fuel ratio correction coefficient FAF by a constant b every predetermined time.

As shown in FIG. 6, when the condition of the feedback control is not satisfied in step 201, the process proceeds to step 230. Then, in step 230, the values of the air-fuel ratio correction coefficient FAF and the old air-fuel ratio correction coefficient FAF0 are set to "1". Thereafter, the process proceeds to step 212, and in the processing of steps 212 to 220, the feedback correction coefficient FAFST for the step motor 14 or the feedback correction coefficient FAFINJ for the injector 17 is determined using the air-fuel ratio correction coefficient FAF.

Next, a "learning routine" executed at step 300 in the processing of the "main routine" described above.
Will be described with reference to the flowchart of FIG. The process of the “learning routine” is executed by calling a subroutine in step 300.

When the processing of this routine is started, first, at step 310, the learning timing flag YKG
Is determined to be “1”. If the learning timing flag YKG is not "1", the process directly proceeds to step 320, where the learning timing flag YKG is set to "0", and the subsequent processing is temporarily terminated. That is, the following process is executed only when the learning timing flag YKG is “1”, that is, only when the air-fuel ratio is switched from rich to lean or from lean to rich.

If the learning timing flag YKG is "1" in step 310,
At 30, it is determined whether or not the injector feedback determination flag YFBINJ is "1", that is, whether or not the vehicle is in a medium / light load state. Here, the determination flag YFB
If INJ is “1”, the process proceeds to step 340 assuming that the vehicle is in the middle / light load state, and steps 340 and 35 are performed.
0, 360, and 320 are executed.

That is, in step 340, “FA
The magnitude of the value of the average air-fuel ratio correction coefficient FAFAV obtained in the processing of the “F calculation routine” is determined. And
In step 340, the average air-fuel ratio correction coefficient FA
If the FAV is "1", it is assumed that the actual air-fuel ratio is the stoichiometric air-fuel ratio, and the learning timing flag YKG is reset to "0" at step 320, and the subsequent processing is temporarily terminated.

If it is determined in step 340 that the average air-fuel ratio correction coefficient FAFAV is greater than "1", then in step 350, a learning correction value KG corresponding to the intake pressure PM at that time is added by a constant i. Then, in step 320, the learning timing flag YKG is reset to "0", and the subsequent processing is temporarily terminated.

Further, when the average air-fuel ratio correction coefficient FAFAV is smaller than "1" in step 340,
In step 360, a constant i is subtracted from the learning correction value KG. Then, in step 320, the learning timing flag YKG is reset to "0", and the subsequent processing is temporarily terminated.

As described above, steps 340 and 3 described above are performed.
By executing a series of processes in 50, 360, and 320 each time the air-fuel ratio switches between lean and rich, the learning correction value KG is increased or decreased by a constant i, and eventually becomes an optimal value for the intake pressure PM at that time. . Then, by using the learning correction value KG, in step 160 of the “ST calculation routine”, the target step number ST in the middle and light load state, that is, in the normal operation or the like is calculated, and “TAU” is calculated.
In step 460 of the “calculation routine”, the target injection time TAU during idle operation or the like is calculated.

On the other hand, if the injector feedback determination flag YFBINJ is not "1" in step 330, that is, if the load is high, the process directly proceeds to step 320 without calculating the learning correction value KG. At 320, the learning timing flag YKG is reset to "0", and the subsequent processing is temporarily terminated.

Next, the processing of the “TAU calculation routine” executed in step 400 in the processing of the aforementioned “main routine” will be described. The processing of the “TAU calculation routine” is a processing that is executed by a subroutine call in step 400, and is shown in the flowchart of FIG.

When the processing of this routine is started, first, at step 410, the basic injection time TAUBSE is calculated. The basic injection time TAUBSE is obtained by referring to a three-dimensional map stored in the ROM 42 in advance based on the values of the engine speed NE and the intake pressure PM detected by the rotation speed sensor 31 and the intake pressure sensor 34.

Next, at step 420, the feedback correction coefficient FAFINJ for the injector 17 calculated in the above-mentioned "FAF calculation routine" processing.
To load.

Further, in step 430, the ROM 42 is set based on the intake air temperature THA detected by the intake air temperature sensor 32.
The intake air temperature correction coefficient FTHAI is calculated with reference to the two-dimensional map stored in advance in FIG.

Further, in step 440, the ROM 4 based on the cooling water temperature THW detected by the water temperature sensor 35 is used.
2, a water temperature correction coefficient FTHWI is calculated with reference to a two-dimensional map stored in advance.

Subsequently, at step 450, the learning correction value K obtained by the above-described "learning routine"
Load G. Then, in step 460,
Basic injection time TA previously calculated or loaded
The basic injection time TAUBSE is corrected by multiplying the UBSE by an intake air temperature correction coefficient FTHAI, a water temperature correction coefficient FTHWI, a feedback correction coefficient FAFINJ for the injector 17 and a learning correction value KG, respectively. Is set as the target injection time TAU. Then, after executing the processing of step 460, the processing of this routine is temporarily terminated.

Using the target step number ST and the target injection time TAU obtained as described above, how to drive and control the step motor 14 and the injector 17 will be described with reference to the flowcharts of FIGS. Will be described.

FIG. 11 shows the "capture interrupt routine".
This is the process. When the process of this routine is started, first, at step 500, the engine speed NE is calculated based on the detection signal of the speed sensor 31.

Next, at step 510, the injector 17 is operated based on the calculated engine speed NE.
It is determined whether or not it is the injection timing. Here, if it is not the injection timing of the injector 17, the subsequent processing is once ended as it is.

If it is determined in step 510 that the injection timing of the injector 17 has been reached, step 52
At 0, energization of the injector 17 is started to open the injector 17.

Further, at step 530, based on the target injection time TAU described above, the power supply end time of the injector 17 is set, and the subsequent processing is temporarily terminated. FIG. 12 shows the processing of the "compare interrupt routine", which is executed at a relatively short predetermined time interval.

When the processing of this routine is started, first, in step 600, it is determined whether or not it is the timing of the energization end time set in step 530 in the processing of the aforementioned “capture interrupt routine”. Here, if it is not the timing, the process directly proceeds to step 620.

If it is determined in step 600 that the current is the end time of the energization, in step 610, the energization of the injector 17 is terminated to close the injector 17, and the process proceeds to step 620.

In step 620 after shifting from step 600 or step 610, it is determined whether or not it is the control timing of the step motor 14 determined in the processing described later. Here, if the control timing is not reached, the subsequent processing is once ended as it is.

On the other hand, when it is the control timing of the step motor 14, in step 630, the processing of the "step motor control routine" is executed. The processing of the "step motor control routine" is shown in the flowchart of FIG. 13, and is executed by calling a subroutine in step 630. When the processing of this routine is started, first, in step 631, the current step number SNOW representing the current step number of the step motor 14 is loaded. This current step number SNO
W is a value written to the backup RAM 44 when the CPU 41 outputs a rotation command value to the step motor 14 via the external output circuit 46.

In step 632, "ST
Target step number ST obtained in the process of "calculation routine"
To load. Then, in step 633, the loaded current step number SNOW and the target step number ST
Compare with. In steps 633 to 637, a process of converging the current step number SNOW indicating the step number of the step motor 14 to the target step number ST is performed.

That is, in step 633, if the target step number ST is equal to the current step number SNOW, there is no need to drive the step motor 14, so that the subsequent processing is temporarily terminated.

If the target step number ST is larger than the current step number SNOW in step 633, a forward rotation command is output to the step motor 14 to increase the step number of the step motor 14 in step 634. Then, the motor 14 is rotated forward by one step.

Subsequently, in step 635, the current step number SNOW is incremented by "1", and the subsequent processing is temporarily terminated. Further, in step 633, if the target step number ST is smaller than the current step number SNOW, in step 636, a reverse rotation command is output to the step motor 14 to reduce the step number of the step motor 14, and 14 is rotated in reverse by one step.

Subsequently, in step 637, the current step number SNOW is decremented by "1", and the subsequent processing is temporarily terminated. Then, by repeatedly executing the series of steps 633 to 637 described above, the number of steps of the step motor 14 is made to converge to the target number of steps ST.

After the processing of the "step motor control routine" is completed as described above, the processing returns to the flowchart of FIG. 12, and in step 640, the next control timing is set. This control timing is determined in step 6
20 is used for the determination, for example, a time obtained by adding a certain time to the current time.

Thereafter, in step 650, the value of the timer counter CNT1 is incremented by "1", and the subsequent processing is temporarily terminated. As described in detail above, according to the air-fuel ratio control device for the LPG engine in this embodiment, when the injector feedback determination flag YFBINJ is “1” in step 212 of the “FAF calculation routine” shown in FIG. That is, L
If the PG engine 1 is in a medium / light load state, step 2
In 13, the feedback correction coefficient FAFST for the step motor 14 is set to "1.0".
Then, based on the target step number ST obtained by using the feedback correction coefficient FAFST, the step motor 14 is drive-controlled to fix the fuel throttle valve 15 at a predetermined closed position, so that the main fuel passage 12 Reduce the fuel supply to fix the air-fuel ratio to the lean side. At the same time, in step 214, the air-fuel ratio correction coefficient FAF obtained at that time is set as the feedback correction coefficient FAFINJ for the injector 17. Then, the feedback correction coefficient FAFINJ
Is controlled based on the injection time TAU obtained by using the air-fuel ratio, and the air-fuel ratio feedback control is performed so that the air-fuel ratio on the lean side becomes the stoichiometric air-fuel ratio.

On the other hand, in step 212 of the "FAF calculation routine", if the injector feedback determination flag YFBINJ is not "1", that is, if the LPG engine 1 is in a high load state, and in step 216, the previous injector When the feedback determination flag YFBINJ0 is “1”, that is, LPG
If the engine 1 is in a medium-to-light load state, step 217
, The air-fuel ratio correction coefficient FAF is reset to “1.0”. That is, when the state is switched from the medium to light load state to the high load state, the air-fuel ratio correction coefficient FAF is initialized to “1.0”. In the next step 218, the initialized air-fuel ratio correction coefficient FAF is
Is set as the feedback correction coefficient FAFST. That is, the feedback correction coefficient FAFST for the step motor 14 is initialized to “1.0”. Then, the initialized feedback correction coefficient FAFS
Based on the target number of steps ST obtained using T,
The drive control of the step motor 14 is started and the fuel throttle valve 1 is started.
5 is started. Thereby, the main fuel passage 12
The air-fuel ratio feedback control is executed such that the main fuel supply amount from the LPG engine 1 starts to be adjusted and the air-fuel ratio of the LPG engine 1 becomes the stoichiometric air-fuel ratio. Further, in step 219, the feedback correction coefficient FAFI for the injector 17
NJ is set to “1.0”. Then, the injector 17 is driven and controlled based on the injection time TAU obtained using the feedback correction coefficient FAFINJ,
The injection amount of the auxiliary fuel is fixed.

That is, in this embodiment, when the LPG engine 1 is switched from the air-fuel ratio feedback control under a medium-to-light load state to the air-fuel ratio feedback control under a high load state, a step corresponding to the switching control mode is performed. The air-fuel ratio correction coefficient FAF used for the motor 14 is initialized to “1.0”.

Therefore, when the control mode is switched, the air-fuel ratio correction coefficient FAF is once initialized to “1.0”, so that the correction amount per unit related to the air-fuel ratio correction coefficient FAF between both control modes. Are different, the feedback correction coefficient F is calculated based on the initialized air-fuel ratio correction coefficient FAF.
AFST is initialized. As a result, immediately after the control mode switching, the air-fuel ratio feedback control by the step motor 14 is appropriately corrected.

As a result, immediately after the switching of the control mode, the deviation of the correction amount due to the feedback correction coefficient FAFST is suppressed as much as possible, and the air-fuel ratio obtained by the feedback control based on the correction coefficient FAFST is greatly deviated. Can be prevented beforehand. Furthermore, as a result, the output of the LPG engine 1 can be stabilized to improve drivability, and deterioration of exhaust emissions can be prevented.

The present invention is not limited to the above-described embodiment, and may be implemented by appropriately changing a part of the configuration without departing from the spirit of the invention. For example, in the above-described embodiment, L is changed from a medium to light load state to a high load state.
Although the air-fuel ratio correction coefficient FAF is initialized to “1.0” when the air-fuel ratio feedback control mode of the PG engine 1 is switched, the air-fuel ratio feedback of the LPG engine 1 is changed from a high load state to a medium to light load state. When the control mode is switched, the air-fuel ratio correction coefficient FAF may be initialized to “1.0”.

[0103]

As described in detail above, according to the present invention,
When the control mode is switched between the air-fuel ratio feedback control based on the main fuel supply under the high load state and the air-fuel ratio feedback control based on the auxiliary fuel supply under the medium-light load state, the control mode is used according to the control mode after the switching. Since the air-fuel ratio correction coefficient is initialized, even if the correction amount per unit related to the air-fuel ratio correction coefficient differs between the two control modes,
The air-fuel ratio immediately after the switching of the control mode is appropriately corrected, and it is possible to prevent the air-fuel ratio at the time of the switching of the control mode from being significantly deviated, thereby improving the drivability and improving the exhaust gas. It has an excellent effect that deterioration of emission can be prevented.

[Brief description of the drawings]

FIG. 1 is a conceptual configuration diagram illustrating a basic conceptual configuration of the present invention.

FIG. 2 is an LPG according to an embodiment of the present invention;
It is a schematic structure figure showing an engine system.

FIG. 3 is a block diagram illustrating a configuration of an electronic control device according to one embodiment.

FIG. 4 is a flowchart illustrating a “main routine” executed by the electronic control unit in one embodiment.

FIG. 5 is a flowchart illustrating an “ST calculation routine” executed by the electronic control unit in one embodiment.

FIG. 6 is a flowchart illustrating a “FAF calculation routine” executed by the electronic control unit in one embodiment.

FIG. 7 is a flowchart illustrating a “FAF calculation routine” executed by the electronic control unit in one embodiment.

FIG. 8 is a flowchart illustrating a “YFBINJ calculation routine” executed by the electronic control unit in one embodiment.

FIG. 9 is a flowchart illustrating a “learning routine” executed by the electronic control unit in one embodiment.

FIG. 10 is a flowchart illustrating a “TAU calculation routine” executed by the electronic control unit in one embodiment.

FIG. 11 is a flowchart illustrating a “capture interrupt routine” executed by the electronic control unit in one embodiment.

FIG. 12 is a flowchart illustrating a “compare interrupt routine” executed by the electronic control unit in one embodiment.

FIG. 13 is a flowchart illustrating a “step motor control routine” executed by the electronic control unit in one embodiment.

[Explanation of symbols]

1 LPG engine, 2 intake passage, 4 venturi,
7: Exhaust passage, 12: Main fuel passage, 14: Step motor, 15: Fuel throttle valve (12, 15 constitute main fuel mixing means), 17: Injector as auxiliary fuel injection means, 33: Throttle Sensor, 34 ... intake pressure sensor (33, 34 constitute load state detecting means),
36 ... Oxygen sensor as air-fuel ratio detecting means, 38 ... ECU which constitutes correction coefficient calculating means, high load control means, medium / light load control means and correction coefficient initialization means.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F02D 41/00-45/00 395

Claims (1)

(57) [Claims] A main fuel mixing means for mixing main fuel and intake air through a venturi formed in an intake passage of an engine using liquefied petroleum gas as fuel, and supplying the mixed gas to the engine; It is provided in the intake passage at a position different from the main fuel mixing means,
An auxiliary fuel injection unit that injects auxiliary fuel into the intake passage; an air-fuel ratio detection unit that is provided in an exhaust passage of the engine and detects an air-fuel ratio of the engine from an oxygen concentration in exhaust gas; Correction coefficient calculation means for calculating an air-fuel ratio correction coefficient based on an air-fuel ratio detected by the air-fuel ratio detection means, in order to correct the mixture supply amount and the auxiliary fuel injection amount from the auxiliary fuel injection means, respectively; Load state detection means for detecting an operation load state of the engine, and when the detection result of the load state detection means is in a high load state, the correction coefficient calculation means calculates an air-fuel mixture supply amount by the main fuel mixing means. A high-load control means for performing air-fuel ratio feedback control by increasing or decreasing the air-fuel ratio based on the calculated air-fuel ratio correction coefficient; At one time, medium-light load control means for performing air-fuel ratio feedback control by increasing or decreasing the auxiliary fuel injection amount from the auxiliary fuel injection means based on the air-fuel ratio correction coefficient calculated by the correction coefficient calculation means. An air-fuel ratio control device for an LPG engine, comprising: when the control mode is switched between the air-fuel ratio feedback control by the high-load control unit and the air-fuel ratio feedback control by the medium-light load control unit, the control mode after the switching An air-fuel ratio control device for an LPG engine, comprising: a correction coefficient initializing means for initializing an air-fuel ratio correction coefficient used in accordance with (1).